Acoustic respiratory monitoring sensor having multiple sensing elements

ABSTRACT

According to certain described aspects, multiple acoustic sensing elements are employed in a variety of beneficial ways to provide improved physiological monitoring, among other advantages. In various embodiments, sensing elements can be advantageously employed in a single sensor package, in multiple sensor packages, and at a variety of other strategic locations in the monitoring environment. According to other aspects, to compensate for skin elasticity and attachment variability, an acoustic sensor support is provided that includes one or more pressure equalization pathways. The pathways can provide an air-flow channel from the cavity defined by the sensing elements and frame to the ambient air pressure.

INCORPORATION BY REFERENCE TO ANY RELATED APPLICATIONS

Any and all applications, if any, for which a foreign or domesticpriority claim is identified in the Application Data Sheet of thepresent application are hereby incorporated by reference under 37 CFR1.57.

Additionally, this application relates to the following U.S. patentapplications, the disclosures of which are incorporated in theirentirety by reference herein:

Filing App. No. Date Title Attorney Docket 60/893,853 Mar. 8, 2007MULTI-PARAMETER PHYSIOLOGICAL MCAN.014PR MONITOR 60/893,850 Mar. 8, 2007BACKWARD COMPATIBLE MCAN.015PR PHYSIOLOGICAL SENSOR WITH INFORMATIONELEMENT 60/893,858 Mar. 8, 2007 MULTI-PARAMETER SENSOR FOR MCAN.016PRPHYSIOLOGICAL MONITORING 60/893,856 Mar. 8, 2007 PHYSIOLOGICAL MONITORWITH MCAN.017PR FAST GAIN ADJUST DATA ACQUISITION 12/044,883 Mar. 8,2008 SYSTEMS AND METHODS FOR MCAN.014A DETERMINING A PHYSIOLOGICALCONDITION USING AN ACOUSTIC MONITOR 61/252,083 Oct. 15, 2009 DISPLAYINGPHYSIOLOGICAL MCAN.019PR INFORMATION 12/904,836 Oct. 14, 2010BIDIRECTIONAL PHYSIOLOGICAL MCAN.019A1 INFORMATION DISPLAY 12/904,823Oct. 14, 2010 BIDIRECTIONAL PHYSIOLOGICAL MCAN.019A2 INFORMATION DISPLAY61/141,584 Dec. 30, 2008 ACOUSTIC SENSOR ASSEMBLY MCAN.030PR 61/252,076Oct. 15, 2009 ACOUSTIC SENSOR ASSEMBLY MCAN.030PR2 12/643,939 Dec. 21,2009 ACOUSTIC SENSOR ASSEMBLY MCAN.030A 12/904,890 Oct. 14, 2010ACOUSTIC RESPIRATORY MCAN.033A2 MONITORING SENSOR HAVING MULTIPLESENSING ELEMENTS 12/904,938 Oct. 14, 2010 ACOUSTIC RESPIRATORYMCAN.033A3 MONITORING SENSOR HAVING MULTIPLE SENSING ELEMENTS 12/904,907Oct. 14, 2010 ACOUSTIC PATIENT SENSOR MCAN.033A4 12/904,789 Oct. 14,2010 ACOUSTIC RESPIRATORY MCAN.034A MONITORING SYSTEMS AND METHODS61/252,062 Oct. 15, 2009 PULSE OXIMETRY SYSTEM WITH LOW MCAN.035PR NOISECABLE HUB 61/265,730 Dec. 1, 2009 PULSE OXIMETRY SYSTEM WITH MCAN.035PR3ACOUSTIC SENSOR 12/904,775 Oct. 14, 2010 PULSE OXIMETRY SYSTEM WITH LOWMCAN.035A NOISE CABLE HUB 12/905,036 Oct. 14, 2010 PHYSIOLOGICALACOUSTIC MCAN.046A MONITORING SYSTEM 61/331,087 May 4, 2010 ACOUSTICRESPIRATION DISPLAY MASIMO.800PR2 61/391,098 Oct. 8, 2010 ACOUSTICMONITOR MCAN-P001

Many of the embodiments described herein are compatible with embodimentsdescribed in the above related applications. Moreover, some or all ofthe features described herein can be used or otherwise combined withmany of the features described in the applications listed above.

BACKGROUND

The “piezoelectric effect” is the appearance of an electric potentialand current across certain faces of a crystal when it is subjected tomechanical stresses. Due to their capacity to convert mechanicaldeformation into an electric voltage, piezoelectric crystals have beenbroadly used in devices such as transducers, strain gauges andmicrophones. However, before the crystals can be used in many of theseapplications they must be rendered into a form which suits therequirements of the application. In many applications, especially thoseinvolving the conversion of acoustic waves into a corresponding electricsignal, piezoelectric membranes have been used.

Piezoelectric membranes are typically manufactured from polyvinylidenefluoride plastic film. The film is endowed with piezoelectric propertiesby stretching the plastic while it is placed under a high-polingvoltage. By stretching the film, the film is polarized and the molecularstructure of the plastic aligned. A thin layer of conductive metal(typically nickel-copper) is deposited on each side of the film to formelectrode coatings to which connectors can be attached.

Piezoelectric membranes have a number of attributes that make theminteresting for use in sound detection, including: a wide frequencyrange of between 0.001 Hz to 1 GHz; a low acoustical impedance close towater and human tissue; a high dielectric strength; a good mechanicalstrength; and piezoelectric membranes are moisture resistant and inertto many chemicals.

Due in large part to the above attributes, piezoelectric membranes areparticularly suited for the capture of acoustic waves and the conversionthereof into electric signals and, accordingly, have found applicationin the detection of body sounds. However, there is still a need for areliable acoustic sensor, particularly one suited for measuring bodilysounds in noisy environments.

SUMMARY

Embodiments of an acoustic sensor and physiological monitoring systemdescribed herein are configured to provide accurate and robustmeasurement of bodily sounds under a variety of conditions, such as innoisy environments or in situations in which stress, strain, or movementcan be imparted onto the sensor with respect to a patient.

While certain embodiments described herein are compatible withsingle-sensing element designs, according to certain aspects, multipleacoustic sensing elements are employed to provide enhanced physiologicalmonitoring. For example, multiple acoustic sensing elements can beincluded in one or more sensor packages coupled to a patient and/or atvarious other locations in the monitoring environment, such as on one ormore sensor packages or other components not coupled to the patient.

In some configurations, a plurality of acoustic sensing elements areadvantageously arranged in a single acoustic sensor package. In somesuch embodiments, physical and/or electrical symmetry between thesensing elements can be exploited. In some cases, for example, theelectrical poles of two or more sensing elements are connected so as toprovide improved electrical shielding, enhanced signal to noise ratio,reduced design complexity and associated cost. In one suchconfiguration, multiple sensing elements are arranged in stack on asensor frame or other support structure. Generally, shielding can bebeneficially achieved using one or more portions that are integral tothe sensing elements rather than using physically separate components.

Systems and methods described herein achieve noise compensation in avariety of ways. For example, sensing elements (or groups thereof) canbe arranged such that a physiological signal sensing element provides aphysiological signal having both a component indicative of a targetphysiological signal (e.g., respiratory, heart or digestive sounds) andan interfering noise component. At least one other sensing element, onthe other hand, provides a reference signal. The reference signal mayinclude a significant noise component, but not a significant targetphysiological component, for example, and can advantageously be used toproduce a physiological signal having a reduced noise component. Forexample, certain embodiments employ adaptive filtering techniques toattenuate the noise component. In various embodiments, the noisecomponent can come from a variety of sources, an can include, withoutlimitation, ambient noise, interfering bodily sounds emanating from thepatient (e.g., respiratory, heart or digestive sounds), noise comingfrom skin-coupled devices (e.g., surgical or other medical equipment),etc., further specific examples of which are provided herein.

Moreover, according certain aspects, the sensing elements areselectively configurable in a plurality of modes. For example, thesensing elements can be configured as either physiological signalsensing elements or noise sensing elements, as desired. As oneillustrative example, a first sensor is used to detect respiratorysounds, while a second sensor used to detect heart sounds. In a firstmonitoring mode, the system uses the first sensor to detect the targetrespiratory sounds, and uses the second sensor as a noise referencesensor to minimize the effect of heart sounds (and/or other interferingnoise) on the respiratory signal. Conversely, the system can switch to asecond mode where the first sensor is used as the reference sensor toreduce the effect of respiratory sounds (and/or other interfering noise)on the signal produced by the second sensor. A wide variety ofembodiments incorporating selective sensing element configurations aredescribed herein.

Additionally, sensing elements (or groups thereof) can be arranged withrespect to one another such that components of their output signalsresulting from a common source (e.g., the patient's body) will becorrelated or otherwise generally similar. The signal components frominterfering noise sources, on the other hand, can be expected to beuncorrelated or otherwise have certain dissimilarities (e.g., phase ortime shift). In these cases, the output signals from the first andsecond acoustic sensing elements can be combined in ways that accentuatecommonalities between the two signals while attenuating differences.

According to yet another aspect of the disclosure, an acoustic sensorincludes one or more sensing elements supported by a frame or othersupport structure. The sensing elements contact the frame at certainlocations and are spaced from the frame at others. The sensing elementsand frame define a cavity in which the sensing elements vibrate inresponse to acoustic signals received from a medical patient. However,skin elasticity and the force used to attach the acoustic sensor to themedical patient's skin can affect the volume and/or air pressure withinthe cavity defined by the sensing elements and frame. Variability inskin elasticity or attachment force can lead to variability in cavityresonance, which can cause unwanted variability in sensor performance.For example, an acoustic sensor that is attached to very elastic skinmay provide a different output signal than an acoustic sensor that isattached to firmer or tighter skin. Similarly, an acoustic sensorloosely attached to patient's skin may provide a different output signalthan an acoustic sensor tightly attached a patient's skin.

To compensate for skin elasticity and attachment variability, in oneembodiment the acoustic sensor support includes one or more pressureequalization pathways. The pathways provide an air-flow channel from thecavity defined by the sensing elements and frame to the ambient airpressure. By equalizing pressure within the cavity with ambient duringsensing, variability in sensor performance may be reduced and/oreliminated. In some embodiments, the pressure equalization pathwaysinclude one or more holes, notches, ports, or channels that extend fromwithin the sensor's cavity to a location in communication with ambientair pressure.

In certain embodiments, a medical device is provided for non-invasivelyoutputting a reduced noise signal responsive to acoustic vibrationsindicative of one or more physiological parameters of a medical patient.In some embodiments, the medical device includes a first acousticsensing element configured to be acoustically coupled to the body of apatient, the first acoustic sensing element being configured to output afirst signal comprising a physiological signal component and a noisecomponent. The medical device can also include a second acoustic sensingelement being configured to output a second signal comprising at least anoise component. The medical device of some embodiments includes a noiseattenuator configured to produce a reduced noise signal in response tothe first and second signals. The reduced noise signal can include aphysiological signal component and a noise component. In certainembodiments, the ratio of the physiological signal component of thereduced noise signal to the noise component of the reduced noise signalis greater than the ratio of the physiological signal component of thefirst signal to the noise component of the first signal.

According to certain aspects, a method of providing a reduced noisesignal responsive to acoustic vibrations indicative of one or morephysiological parameters of a medical patient is provided. The methodcan include outputting a first signal using first acoustic sensingelement coupled to the body of a patient. The signal may comprise aphysiological component and a noise component. The method can furtherincluding outputting a second signal using the second acoustic sensingelement, the second signal comprising at least a noise component. Incertain embodiments, the method further includes processing the firstand second signals using a noise attenuator to produce a reduced noisesignal in response to the first and second signals. The reduced noisesignal can include a physiological signal component and a acoustic noisecomponent. In certain embodiments, the ratio of the physiological signalcomponent of the reduced noise signal to the noise component of thereduced noise signal greater than the ratio of the physiological signalcomponent of the first signal to the noise component of the firstsignal.

In certain embodiments, a medical device is provided for non-invasivelygenerating a reduced noise signal responsive to acoustic vibrationsindicative of one or more physiological parameters of a medical patient.The medical device can include at least one first acoustic sensingelement configured to generate a first signal in response to acousticvibrations. The medical device of certain embodiments also includes atleast one second acoustic sensing element configured to generate asecond signal in response to acoustic vibrations. In certainembodiments, the medical device further includes a noise attenuationmodule configured to generate a reduced noise signal indicative of oneor more physiological parameters of a medical patient in response to atleast one of the first and second signals.

A medical sensor is provided in some embodiments for non-invasivelyoutputting signals responsive to acoustic vibrations indicative of oneor more physiological parameters of a medical patient. The medicalsensor can include a first acoustic sensing element for generating afirst signal. The medical sensor can also include a second acousticsensing element for generating a second signal. The first and secondsignals in some embodiments are configured to be provided to a noiseattenuator adapted to reduce a noise component of the first or secondsignal.

In certain embodiments, an acoustic sensor is provided fornon-invasively outputting signals responsive to acoustic vibrationsindicative of one or more physiological parameters of a medical patient.In certain embodiments, the acoustic sensor includes a sensor support.The acoustic sensor can also include a first acoustic sensing element atleast partially supported by the sensor support and configured to outputa first signal responsive to acoustic vibrations. The acoustic sensor ofsome embodiments includes a second acoustic sensing element at leastpartially supported by the sensor support and configured to output asecond signal responsive to acoustic vibrations. In some embodiments,the first and second acoustic sensing elements are configured to providethe first and second signals to a noise attenuator configured to outputa reduced noise signal having a higher signal to noise ratio than eitherof the first and second signals.

In certain embodiments, a method is provided of non-invasivelyoutputting signals responsive to acoustic vibrations indicative of oneor more physiological parameters of a medical patient. The method caninclude providing a sensor comprising a sensor support, a first acousticsensing element at least partially supported by the sensor support, anda second acoustic sensing element at least partially supported by thesensor support. The method can further include outputting a first signalusing the first acoustic sensing element. In certain embodiments, thefirst signal is responsive to acoustic vibrations, and the firstacoustic sensing element is coupled to a medical patient. The method caninclude outputting a second signal using the second acoustic sensingelement. In certain embodiments, the second signal responsive toacoustic vibrations, and the second acoustic sensing element coupled tothe medical patient. In certain embodiments, the method includesproviding the first signal and the second signal to a noise attenuatorconfigured to output a reduced noise signal having a higher signal tonoise ratio than either of the first and second signals.

In certain embodiments, an acoustic sensor is provided fornon-invasively outputting signals responsive to acoustic vibrationsindicative of one or more physiological parameters of a medical patient.The acoustic sensor can include a sensor support, and a firstpiezoelectric film at least partially supported by the sensor supportand comprising a first electrode and a second electrode. In certainembodiments, the sensor includes a second piezoelectric film at leastpartially supported by the sensor support and comprising a firstelectrode and second electrode. In some embodiments, the first electrodeof the first piezoelectric film and the first electrode of the secondpiezoelectric film are coupled to a common potential, and the secondelectrode of the first piezoelectric film and the second electrode ofthe second piezoelectric film are coupled to a noise attenuator.

In certain embodiments, an acoustic sensor is provided fornon-invasively outputting signals responsive to acoustic vibrationsindicative of one or more physiological parameters of a medical patient.In some embodiments, the acoustic sensor includes a sensor support. Insome embodiments, the acoustic sensor includes a first acoustic sensingelement at least partially supported by the sensor support andcomprising an inner portion and an outer portion. In some embodiments,the acoustic sensor includes a second acoustic sensing element at leastpartially supported by the sensor support and comprising an innerportion and an outer portion. In certain embodiments, the acousticsensor is configured such that the inner portions are positioned betweenthe outer portions, the outer portions forming an electrical shieldingbarrier around the inner portions.

In certain embodiments, a method is provided of manufacturing anacoustic sensor for non-invasively outputting signals responsive toacoustic vibrations indicative of one or more physiological parametersof a medical patient. The method can include providing a first acousticsensing element comprising an inner portion and an outer portion. Themethod can also include providing a second acoustic sensing elementcomprising an inner portion and an outer portion. In certainembodiments, the method includes attaching the first acoustic sensingelement to a sensor support. The method in some embodiments includesattaching the second sensing element to the sensor support over thefirst acoustic sensing element. In certain embodiments, the innerportions of the first and second acoustic sensing elements are disposedbetween the outer portions of the first and second acoustic sensingelements, and the outer portions form an electrical shielding barrieraround the inner portions.

An acoustic sensor is provided in some embodiments that is configured tonon-invasively detect acoustic vibrations associated with a medicalpatient, the acoustic vibrations indicative of one or more physiologicalparameters of the medical patient. The sensor can include a sensorsupport and first and second sensing membranes supported by the sensorsupport, each of said first and second sensing membranes comprisingfirst and second surfaces on opposite sides of each of said first andsecond sensing membranes. In some embodiments, the first and secondsensing membranes are aligned such that said first surfaces face eachother. The first surfaces in some embodiments are configured to providean electrical signal indicative of a physiological parameter of amedical patient, and said second surfaces are configured to provideelectrical shielding around said first surfaces.

In some embodiments, an acoustic sensor is provided that is configuredto non-invasively detect acoustic vibrations associated with a medicalpatient. The acoustic vibrations can be indicative of one or morephysiological parameters of the medical patient. In certain embodiments,the sensor includes at least one sound-sensing membrane is configured todetect acoustic vibrations associated with a medical patient when theacoustic sensor is attached to the medical patient. The sensor can alsoinclude a sensor support defining an acoustic cavity and configured tosupport the at least one sensing membrane over the acoustic cavity. Thesensor support may include at least one pressure equalization pathwayformed in a wall of the sensor support, the at least one pressureequalization pathway extending from the acoustic cavity to ambient airpressure.

In certain embodiments, an acoustic sensor is configured tonon-invasively detect acoustic vibrations associated with a medicalpatient, the acoustic vibrations indicative of one or more physiologicalparameters of the medical patient. The sensor can include at least onesound-sensing membrane configured to detect acoustic vibrationsassociated with a medical patient when the acoustic sensor is attachedto the medical patient. The sensor can further include a sensor supportconfigured to support the at least one sensing membrane against themedical patient's skin. In some embodiments, the sensor is configured toprovide an electrical signal in response to acoustic vibrations detectedby the at least one sound-sensing membrane substantially independent ofa force used to attach the sensor to the medical patient's skin.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages can beachieved in accordance with any particular embodiment of the inventionsdisclosed herein. Thus, the inventions disclosed herein can be embodiedor carried out in a manner that achieves or optimizes one advantage orgroup of advantages as taught herein without necessarily achieving otheradvantages as can be taught or suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the drawings, reference numbers can be re-used to indicatecorrespondence between referenced elements. The drawings are provided toillustrate embodiments of the inventions described herein and not tolimit the scope thereof.

FIGS. 1A-B are block diagrams illustrating physiological monitoringsystems in accordance with embodiments of the disclosure.

FIG. 1C is a top perspective view illustrating portions of a sensorsystem in accordance with an embodiment of the disclosure.

FIGS. 2A-2B are block diagrams of example embodiments of patient sensorsthat including first and second physiological signal acoustic sensingelements and at least one acoustic coupler for acoustically couplingboth of the first and second physiological signal acoustic sensingelements to a patient's body.

FIG. 3A is a schematic illustration of an embodiment of a circuit forimproving signal-to-noise ratio by combining physiological signals fromtwo or more acoustic sensing elements.

FIG. 3B is a schematic illustration of an embodiment of a circuit forimproving signal-to-noise ratio by combining physiological signals fromtwo or more acoustic sensing elements arranged in a stackedconfiguration.

FIG. 4A is a cross-sectional schematic drawing of an embodiment of anacoustic sensor that includes first and second acoustic sensing elementsin a stacked configuration.

FIG. 4B shows a cross-sectional schematic drawing of a portion of thefirst and second stacked sensing elements of FIG. 4A.

FIGS. 5A-5D show views of example acoustic sensing elements havingelectrode coating configurations tailored for use in a stackedconfiguration.

FIGS. 6A-6B are top and bottom exploded, perspective views,respectively, of a sensor incorporating multiple sensing elements inaccordance with embodiments described herein.

FIG. 7 is a block diagram of an example acoustic physiologicalmonitoring system having noise compensation features.

FIG. 8 is a block diagram of an embodiment of an acoustic physiologicalmonitoring system with an acoustic sensor that includes first and secondacoustic sensing elements.

FIG. 9A is a block diagram of an embodiment of an acoustic physiologicalmonitoring system with first and second acoustic sensing elementsdisposed in separate acoustic sensors.

FIG. 9B is a block diagram of an embodiment of an acoustic physiologicalmonitoring system with an acoustic sensor that includes a first acousticsensing element, and a physiological monitor unit that includes a secondacoustic sensing element.

FIGS. 9C-9D illustrate example systems including dual acoustic sensorsapplied to a patient according to certain embodiments.

FIG. 10 is a block diagram of an embodiment of an acoustic sensor thatincludes a physiological signal acoustic sensing element with anacoustic coupler for acoustically coupling it to a patient's body, and anoise acoustic sensing element.

FIG. 11 is a block diagram of an embodiment of an acoustic sensor thatincludes a physiological signal acoustic sensing element with anacoustic coupler for increasing acoustic coupling between it and apatient's body, and a noise acoustic sensing element with an acousticdecoupler for decreasing acoustic coupling between it and the patient'sbody.

FIG. 12 is a cross-sectional schematic drawing of an embodiment of anacoustic sensor that includes a physiological signal acoustic sensingelement and a noise acoustic sensing element.

FIG. 13 is a cross-sectional schematic drawing of another embodiment ofan acoustic sensor that includes a physiological signal acoustic sensingelement and a noise acoustic sensing element.

FIG. 14 is a cross-sectional schematic drawing of another embodiment ofan acoustic sensor that includes a physiological signal acoustic sensingelement and a noise acoustic sensing element.

FIG. 15 is a cross-sectional schematic drawing of an embodiment of anacoustic sensor that includes a piezoelectric physiological signalacoustic sensing element and a separate noise microphone.

FIG. 16 illustrates a time plot of an acoustic physiological signalcorrupted by noise, as well as a time plot of the noise.

FIG. 17 is a block diagram an embodiment of a noise attenuator of anacoustic physiological monitoring system.

FIG. 18 is a block diagram of an embodiment of a signal qualitycalculator in an acoustic physiological monitoring system.

FIG. 19A is a top perspective view illustrating portions of a sensorassembly in accordance with an embodiment of the disclosure.

FIGS. 19B-19C are top and bottom perspective views, respectively, of asensor including a sensor subassembly and an attachment subassembly ofFIG. 19A.

FIGS. 19D-19E are top and bottom exploded, perspective views,respectively, of the sensor subassembly of FIGS. 19A-19C.

FIG. 19F shows a top perspective view of an embodiment of a supportframe.

FIG. 20A a perspective view of a sensing element according to anembodiment of the disclosure usable with the sensor assembly of FIG.19A.

FIG. 20B is a cross-sectional view of the sensing element of FIG. 20Aalong the line 20B-20B.

FIG. 20C is a cross-sectional view of the sensing element of FIGS. 20A-Bshown in a wrapped configuration.

FIG. 21 is a cross-sectional view of the coupler of FIGS. 19A-19E takenalong the line 21-21 shown in FIG. 19D.

FIGS. 22A-22B are cross-sectional views of the sensor subassembly ofFIGS. 19B-19C along the lines 22A-22A and 22B-22B, respectively.

FIG. 23A is a top perspective view illustrating portions of a sensorassembly in accordance with another embodiment of the disclosure.

FIGS. 23B-23C are top and bottom perspective views, respectively, of asensor including a sensor subassembly and an attachment subassembly ofFIG. 23A.

FIGS. 23D-23E are top and bottom exploded, perspective views,respectively, of the sensor subassembly of FIGS. 23A-C.

DETAILED DESCRIPTION

Various embodiments will be described hereinafter with reference to theaccompanying drawings. These embodiments are illustrated and describedby example only, and are not intended to be limiting.

Overview

In various embodiments, an acoustic sensor configured to operate with aphysiological monitoring system includes an acoustic signal processingsystem that measures and/or determines any of a variety of physiologicalparameters of a medical patient. For example, in an embodiment, thephysiological monitoring system includes an acoustic monitor. Theacoustic monitor may be an acoustic respiratory monitor which candetermine any of a variety of respiratory parameters of a patient,including respiratory rate, expiratory flow, tidal volume, minutevolume, apnea duration, breath sounds, riles, rhonchi, stridor, andchanges in breath sounds such as decreased volume or change in airflow.In addition, in some cases the acoustic signal processing systemmonitors other physiological sounds, such as heart rate to help withprobe off detection, heart sounds (S1, S2, S3, S4, and murmurs), andchange in heart sounds such as normal to murmur or split heart soundsindicating fluid overload. Moreover, the acoustic signal processingsystem may (1) use a second probe over the chest for additional heartsound detection; (2) keep the user inputs to a minimum (example,height); and/or (3) use a Health Level 7 (HL7) interface toautomatically input patient demography.

In certain embodiments, the physiological monitoring system includes anelectrocardiograph (ECG or EKG) that measures and/or determineselectrical signals generated by the cardiac system of a patient. The ECGincludes one or more sensors for measuring the electrical signals. Insome embodiments, the electrical signals are obtained using the samesensors used to obtain acoustic signals.

In still other embodiments, the physiological monitoring system includesone or more additional sensors used to determine other desiredphysiological parameters. For example, in some embodiments, aphotoplethysmograph sensor determines the concentrations of analytescontained in the patient's blood, such as oxyhemoglobin,carboxyhemoglobin, methemoglobin, other dyshemoglobins, totalhemoglobin, fractional oxygen saturation, glucose, bilirubin, and/orother analytes. In other embodiments, a capnograph determines the carbondioxide content in inspired and expired air from a patient. In otherembodiments, other sensors determine blood pressure, pressure sensors,flow rate, air flow, and fluid flow (first derivative of pressure).Other sensors may include a pneumotachometer for measuring air flow anda respiratory effort belt. In certain embodiments, these sensors arecombined in a single processing system which processes signal outputfrom the sensors on a single multi-function circuit board.

Referring to the drawings, FIGS. 1A through 1C illustrate examplepatient monitoring systems, sensors, and cables that can be used toprovide acoustic physiological monitoring of a patient, such asrespiratory monitoring. FIGS. 2A-18 illustrate embodiments of sensorsand systems, such as those incorporating multiple acoustic sensingelements to provide certain beneficial results, including enhancedsignal-to-noise ratio (SNR), electrical shielding and noisecompensation, for example. Embodiments of FIGS. 2A-18 can be implementedat least in part using the systems and sensors described in FIGS. 1Athrough 1C. FIGS. 19A-23E show additional acoustic sensors andassociated components compatible with embodiments described herein.

Turning to FIG. 1A, an embodiment of a physiological monitoring system10 is shown. In the physiological monitoring system 10, a medicalpatient 12 is monitored using one or more sensor 13, each of whichtransmits a signal over a cable 15 or other communication link or mediumto a physiological monitor 17. The physiological monitor 17 includes aprocessor 19 and, optionally, a display 11. The one or more sensors 13include sensing elements such as, for example, acoustic piezoelectricdevices, electrical ECG leads, pulse oximetry sensors, or the like. Thesensors 13 can generate respective signals by measuring a physiologicalparameter of the patient 12. The signals are then processed by one ormore processors 19. The one or more processors 19 then communicate theprocessed signal to the display 11. In an embodiment, the display 11 isincorporated in the physiological monitor 17. In another embodiment, thedisplay 11 is separate from the physiological monitor 17. In oneembodiment, the monitoring system 10 is a portable monitoring system. Inanother embodiment, the monitoring system 10 is a pod, without adisplay, that is adapted to provide physiological parameter data to adisplay.

For clarity, a single block is used to illustrate the one or moresensors 13 shown in FIG. 1A. It should be understood that the sensor 13shown is intended to represent one or more sensors. In an embodiment,the one or more sensors 13 include a single sensor of one of the typesdescribed below. In another embodiment, the one or more sensors 13include at least two acoustic sensors. In still another embodiment, theone or more sensors 13 include at least two acoustic sensors and one ormore ECG sensors, pulse oximetry sensors, bioimpedance sensors,capnography sensors, and the like. In each of the foregoing embodiments,additional sensors of different types are also optionally included.Other combinations of numbers and types of sensors are also suitable foruse with the physiological monitoring system 10.

In some embodiments of the system shown in FIG. 1A, all of the hardwareused to receive and process signals from the sensors are housed withinthe same housing. In other embodiments, some of the hardware used toreceive and process signals is housed within a separate housing. Inaddition, the physiological monitor 17 of certain embodiments includeshardware, software, or both hardware and software, whether in onehousing or multiple housings, used to receive and process the signalstransmitted by the sensors 13.

As shown in FIG. 1B, the acoustic sensor 13 can include a cable 25. Thecable 25 can include three conductors within an electrical shielding.One conductor 26 can provide power to a physiological monitor 17, oneconductor 28 can provide a ground signal to the physiological monitor17, and one conductor 28 can transmit signals from the sensor 13 to thephysiological monitor 17. For multiple sensors 103, one or moreadditional cables 115 can be provided.

In some embodiments, the ground signal is an earth ground, but in otherembodiments, the ground signal is a patient ground, sometimes referredto as a patient reference, a patient reference signal, a return, or apatient return. In some embodiments, the cable 25 carries two conductorswithin an electrical shielding layer, and the shielding layer acts asthe ground conductor. Electrical interfaces 23 in the cable 25 canenable the cable to electrically connect to electrical interfaces 21 ina connector 20 of the physiological monitor 17. In another embodiment,the sensor 13 and the physiological monitor 17 communicate wirelessly.

FIG. 1C illustrates an embodiment of a sensor system 100 including asensor 101 suitable for use with any of the physiological monitors shownin FIGS. 1A and 1B. The sensor system 100 includes a sensor 101, asensor cable 117, a patient anchor 103 attached to the sensor cable 117,and a connector 105 attached to the sensor cable 117. The sensor 101includes a shell 102 configured to house certain componentry of thesensor 101, and an attachment subassembly 104 positioned the sensor 101and configured to attach the sensor 101 to the patient.

The sensor 101 can be removably attached to an instrument cable 111 viaan instrument cable connector 109. The instrument cable 111 can beattached to a cable hub 120, which includes a port 121 for receiving aconnector 112 of the instrument cable 111 and a second port 123 forreceiving another cable. In certain embodiments, the second port 123 canreceive a cable connected to a pulse oximetry or other sensor. Inaddition, the cable hub 120 could include additional ports in otherembodiments for receiving additional cables. The hub includes a cable122 which terminates in a connector 124 adapted to connect to aphysiological monitor (not shown). In another embodiment, no hub isprovided and the acoustic sensor 101 is connected directly to themonitor, via an instrument cable 111 or directly by the sensor cable117, for example.

The component or group of components between the sensor 101 and themonitor in any particular embodiment may be referred to generally as acabling apparatus. For example, where one or more of the followingcomponents are included, such components or combinations thereof may bereferred to as a coupling apparatus: the sensor cable 117, the connector105, the cable connector 109, the instrument cable 111, the hub 120, thecable 122, and/or the connector 124. It should be noted that one or moreof these components may not be included, and that one or more othercomponents may be included between the sensor 101 and the monitor,forming the cabling apparatus.

The acoustic sensor 101 can further include circuitry for detecting andtransmitting information related to biological sounds to thephysiological monitor. These biological sounds can include heart,breathing, and/or digestive system sounds, in addition to many otherphysiological phenomena. The acoustic sensor 101 in certain embodimentsis a biological sound sensor, such as the sensors described herein. Insome embodiments, the biological sound sensor is one of the sensors suchas those described in U.S. patent application Ser. No. 12/044,883, filedMar. 7, 2008, which is incorporated in its entirety by reference herein(the '883 application). In other embodiments, the acoustic sensor 101 isa biological sound sensor such as those described in U.S. Pat. No.6,661,161 or U.S. patent application Ser. No. 12/643,939, filed on Dec.21, 2009 (the '939 application), both of which are incorporated byreference herein in their entirety. Other embodiments include othersuitable acoustic sensors. For example, in certain embodiments,compatible acoustic sensors can be configured to provide a variety ofauscultation functions, including live and/or recorded audio output(e.g., continuous audio output) for listening to patient bodily orspeech sounds. Examples of such sensors and sensors capable of providingother compatible functionality can be found in U.S. patent applicationSer. No. 12/905,036 embodiment, the sensing elements 920, 921 can beconfigured to sense and process ultrasonic signals (e.g., for ultrasonicimaging). Examples of sensors capable of various types, entitledPHYSIOLOGICAL ACOUSTIC MONITORING SYSTEM, filed on Oct. 14, 2010, whichis incorporated by reference herein in its entirety.

In an embodiment, the acoustic sensor 101 includes one or more sensingelements (not shown), such as, for example, a piezoelectric device orother acoustic sensing device. Where a piezoelectric membrane is used, athin layer of conductive metal can be deposited on each side of the filmas electrode coatings, forming electrical poles. The opposing surfacesor poles may be referred to as an anode and cathode, respectively. Eachsensing element can generate a voltage potential across the electricalpoles that is responsive to vibrations generated by the patient.

The shell 102 according to certain embodiments houses a frame (notshown) or other support structure configured to support variouscomponents of the sensor 101. The one or more sensing elements can begenerally wrapped in tension around the frame. For example, the sensingelements can be positioned across an acoustic cavity disposed on thebottom surface of the frame. Thus, the sensing elements according tosome embodiments are free to respond to acoustic waves incident uponthem, resulting in corresponding induced voltages across the poles ofthe sensing elements.

Additionally, the shell 102 can include an acoustic coupler not shown),which advantageously improves the coupling between the source of thesignal to be measured by the sensor (e.g., the patient's body) and thesensing element. The acoustic coupler of one embodiment includes a bumppositioned to apply pressure to the sensing element so as to bias thesensing element in tension. For example, the bump can be positionedagainst the portion of the sensing element that is stretched across thecavity of the frame.

The attachment sub-assembly 104 in some embodiments includes first andsecond elongate portions 106, 108. The first and second elongateportions 106, 108 can include patient adhesive (e.g., in someembodiments, tape, glue, a suction device, etc.). The adhesive on theelongate portions 106, 108 can be used to secure the sensor subassembly102 to a patient's skin. One or more resilient backbone members 110included in the first and/or second elongate portions 106, 108 canbeneficially bias the sensor subassembly 102 in tension against thepatient's skin and/or reduce stress on the connection between thepatient adhesive and the skin.

While an example sensor system 100 has been provided, embodimentsdescribed herein are compatible with a variety of sensors and associatedcomponents. For example, compatible acoustic couplers, support frames,attachment subassemblies, sensing elements, and other components aredescribed with respect to FIGS. 19-23 below and in the '939 application.

Improving Signal-to-Noise Ratio Using Multiple Sensors

FIG. 2A is a block diagram of an embodiment of a patient sensor 215 thatincludes first and second physiological signal acoustic sensing elements220, 221. The sensing elements 220, 221 are generally adapted to detectphysiological sounds from a patient 201, and can be any of the sensingelements described herein, such as piezoelectric membranes.

The patient sensor 215 can also include at least one acoustic couplerfor acoustically coupling the first and second physiological signalacoustic sensing elements 220, 221 to a patient's body 201. In FIG. 2,both acoustic sensing elements 220, 221 are acoustically coupled to thepatient. As shown in FIG. 1C, the acoustic coupling can be achievedusing a single acoustic coupler 212 for both sensing elements.

According to one configuration, the acoustic sensing elements 220, 221are supported in a stacked configuration on a sensor frame (not shown)or other support. Example stacked configurations are described belowwith respect to FIGS. 3B, 4A-4B and 6A-6B.

As shown in FIG. 2B, first and second acoustic couplers 213, 214 can beused in alternative embodiments. The acoustic couplers 213, 214 can besimilar, for example, to the others described herein. In someembodiments, the acoustic sensing elements 220, 221 are supported in aside-by-side configuration on a frame, similar to what is illustrated inFIG. 14 below (except that both sensing elements 220, 221 areacoustically coupled to the body of the patient, whereas only one of thesensing elements 1420, 1421 is coupled to the body in FIG. 14). In otherembodiments, no acoustic coupler is included.

In some embodiments, the acoustic coupler, or couplers, 213, 214 aredesigned to provide a substantially equal amount of coupling betweeneach of the sensing elements 220, 221 and the patient's body 201, thoughthis is not required. Example acoustic couplers compatible with thesensor 215 are described in greater detail throughout the disclosure.

As described, the first and second physiological signal acoustic sensingelements 220, 221 can be specially adapted to detect physiologicalsounds from a patient. However, the signals output by the acousticsensing elements 220, 221 may also include noise (e.g., random noise,white Gaussian noise, etc.) from a variety of sources, which decreasesthe signal-to-noise ratio (SNR) of the signals.

The SNR of these signals can be improved, however, by collecting thedesired physiological signal from more than one acoustic sensingelement, and then combining (e.g., summing, subtracting, averaging,etc.) the respective outputs from the acoustic sensing elements in amanner that tends to reinforce the physiological signal components ofthe signals while tending to cancel or reduce the noise components ofthe signals. For example, the sensor 215, monitor, or other intermediatecomponent, can include a noise attenuator which performs the combiningof the signals from the sensing elements 220, 221 to achieve theimproved SNR signal. Some embodiments of this approach are illustratedin FIGS. 3A-3B, 4A-4B and 6A-6B.

Generally, where sensors, sensing elements, couplers, etc., aredescribed throughout the disclosure as being coupled to the patient'sbody, this may mean that one or more of the acoustic couplers aredirectly coupled to the patient's skin or other body part, such as wherean acoustic coupler 212 is directly coupled to the skin 201 andtransmits acoustic signals to one or more sensing elements 220, 221 asshown in FIG. 2A. However, this is not necessarily the case. Forexample, in some embodiments, the entire sensor, including couplers,where used, and/or sensing elements may be spaced from the patient'sbody and still receive acoustic signals emanating from the patient.

FIG. 3A is a schematic illustration of an embodiment of a circuit forimproving signal-to-noise ratio by combining physiological signals fromtwo or more acoustic sensing elements 320, 321. The two acoustic sensingelements 320, 321 may be acoustically coupled to the patient's body. Insome embodiments, each of the first and second physiological signalacoustic sensing elements 320, 321 is a piezoelectric film, each havingan anode and a cathode. The acoustic sensing elements 320, 321 detectphysiological sounds from the patient's body and generate electricalwaveforms corresponding to the physiological sounds. Example compatiblepiezoelectric films are described herein, with respect to FIGS. 4A-4B,5A-5D, 6A-6B and 20A-20C, for example.

In FIG. 3A, the piezoelectric films 320, 321 are configured so as togenerate output signals where the physiological signal components are180° or approximately 180° out of phase. For example, in FIG. 3, theacoustic sensing elements 320, 321 generate voltage waveforms 330, 331in response to physiological sounds from the patient. In the figure, thevoltage waveform 330 is a positive pulse, while the voltage waveform 331is a negative pulse, 180° out of phase from the positive pulse 330. Eachof the physiological signal acoustic sensing elements 320, 321 iscommunicatively coupled to a sensing circuit 340. For example, thesensing circuit 340 may comprise or be referred to as a noiseattenuator. Other example noise attenuators are described below withrespect to FIGS. 7, 8, 9, and/or 17, for example. In the illustratedembodiment, the sensing circuit 340 is a difference amplifier, thoughother sensing circuits 340 can be used.

In some embodiments, the 180° phase shift between the outputs from thetwo piezoelectric films 320, 321 is achieved by differentiallyconnecting the piezoelectric films to the difference amplifier 340. Forexample, the cathode 320 b of the first piezoelectric film 320 can beconnected to the non-inverting terminal of the difference amplifier,while the anode 321 a of the second piezoelectric film 321 can beconnected to the inverting terminal of the difference amplifier 340. Theanode 320 a and the cathode 321 b of the first and second films 320,321, respectively, can be connected to ground (or be otherwiseoperatively coupled or coupled to a common potential). In someembodiments, the 180° phase shift is facilitated by mounting the twopiezoelectric films 320, 321 such that one is flipped with respect tothe other. For example, the two piezoelectric films 320, 321 can bemounted such that the cathode of one of the films faces toward thepatient's body, while the anode of the other film faces toward thepatient's body.

Since, in some embodiments, the physiological signal component of thesecond voltage waveform 331 is substantially a negative copy of thephysiological signal component of the first voltage waveform 330, whenthese two waveforms 330, 331 are subtracted by the sensing circuit 340,they combine constructively, as indicated by the output waveform 341from the sensing circuit 340. However, the outputs from the first andsecond piezoelectric films 320, 321 may also each include a noisecomponent (not illustrated in the waveforms 330, 331). If the noise inthe outputs from the piezoelectric films is random or otherwiseuncorrelated, then at least a portion of the noise will tend to becombined destructively by the sensing circuit 340. Thus, the sensingcircuit 340 can amplify the physiological signal component from thefirst and second piezoelectric films 320, 321 while attenuating randomnoise. The result in certain embodiments is that the physiologicalsignal is emphasized while the random noise component of the outputsignals from the piezoelectric films 320, 321 is deemphasized.

For example, in one embodiment, the physiological signal is at leastapproximately doubled while the noise component is increased but lessthan doubled. The noise component might not double due to the random oruncorrelated nature of the noise, resulting in some portions of thenoise combining additively while others combine negatively. Because theincrease in the physiological signal can be greater than the increase inthe noise, the sensor assembly configuration shown in FIG. 3A canimprove signal to noise ratio (SNR).

While the configuration of FIG. 3A shows sensing elements 320, 321 in aside-by-side configuration, other configurations are possible. Forexample, FIG. 3B illustrates an embodiment of a circuit for improvingsignal-to-noise ratio where the sensing elements 320, 321 are in astacked configuration with respect to one another. As described infurther detail below with respect to FIGS. 4A-5B, the first sensingelement 320 may be wrapped around a frame, and the second sensingelement 321 may be wrapped around the first sensing element 320 and theframe.

Similar to the sensor configuration of FIG. 3A, the cathode 320 b of thefirst piezoelectric film 320 can be connected to the non-invertingterminal of the sensing circuit 340, while the anode 321 a of the secondpiezoelectric film 321 can be connected to the inverting terminal of thesensing circuit 340. Thus, in the illustrated embodiment the innerelectrodes 320 b, 321 a of the first and second sensing elements 320,321 generally face one another in the stacked configuration. The innerelectrodes 320 b, 321 a are shown connected to the terminals of thesensing circuit 340, while the outer electrodes 320 a, 321 b areconnected to ground.

Depending on the embodiment, the configuration shown in FIG. 3B canprovide similar improved SNR advantages as described above with respectto FIG. 3A. In addition, as described herein (e.g., with respect toFIGS. 4A-6B), such a configuration can also provide enhanced electricalshielding. For example, the outer electrodes 320 a, 321 b of the sensingelements 320, 321, respectively, can be used to shield the innerelectrodes 320 b, 321 a from electrical noise. As used herein, the terms“shield,” “shielding,” and the like, in addition to having theirordinary meaning, can mean reducing or attenuating noise, rather thancompletely eliminating noise. However, in some embodiments, the terms“shield,” “shielding,” and the like can also mean completely eliminatingnoise.

Generally, a variety of different sensing circuits 340 can be used inthe embodiments of FIGS. 3A-3B and in generally any of the embodimentsdescribed herein where appropriate. Moreover, depending on the sensingcircuit 340 used, the electrodes can be connected in a number ofarrangements to achieve a similar SNR improvement. For example, asimilar result could be obtained by connecting either both anodes orboth cathodes, of the piezoelectric films 320, 321 to the inputs of asumming amplifier instead of a sensing circuit. In such embodiments, thephysiological signal components of the outputs from the piezoelectricfilms can be approximately in phase and, therefore, can combineconstructively when added by the summing amplifier. Still, at least aportion of random noise from the two output signals from thepiezoelectric films 320, 321 will combine destructively, therebyattenuating noise and improving SNR. In some embodiments, more than twophysiological signal acoustic sensing elements are used, and theirinputs are summed together by, for example, a summing amplifier, adigital signal processor, etc. In some embodiments, one or more of theouter electrodes 320 a, 321 b can be operatively coupled to the sensingcircuit 340, and one or more of the inner electrodes 320 b, 321 a areconnected to ground. In yet other embodiments, the sensing circuit 340comprises a coupling junction coupling together one or more of theelectrodes of the respective sensing elements 320, 321.

Moreover, the number and arrangement of the sensing elements 320, 321can vary according to certain aspects. For example, in some embodiments,more than two physiological signal acoustic sensing elements 320, 321are used, and their inputs are summed together by, for example, asumming amplifier, a digital signal processor, etc. A variety ofconfigurations including more than two sensing elements are possible.For example, in one embodiment a pair of stacked sensing elements isarranged in a side-by-side configuration on a frame with respect toanother pair of stacked sensing elements. In other embodiments, morethan two sensing elements (e.g., 3, 4, 5 or more) are arranged in astacked configuration. In yet other embodiments, more than two sensingelements (e.g., 3, 4, 5 or more) are arranged side-by-side with respectto one another.

FIG. 4A is a cross-sectional schematic drawing of an embodiment of anacoustic sensor 415 that includes first and second acoustic sensingelements 420, 421 in a stacked configuration. When connected to asensing circuit (not shown, e.g., a difference amplifier) in the mannerdescribed above with respect to FIG. 3B, the acoustic sensor 415 canadvantageously provide improved signal-to-noise ratio.

In the depicted embodiment, the first acoustic sensing element 420 iswrapped around a portion of the frame 418 and the second acousticsensing element 421 is generally wrapped around the first acousticsensing element 420 and also supported by the frame. In the illustratedembodiment, the physiological signal acoustic sensing elements 420, 421are piezoelectric films. An acoustic coupler 414 acoustically couplesthe sensing elements 420, 421 to the patient's body 401, and can bealigned with both the first and second sensing elements 420, 421, asshown. In some other embodiments, an acoustic coupler 414 is not used.In the embodiment of FIG. 4A, the two piezoelectric films 420, 421 bothextend over the acoustic cavity 436 of the frame 2118. Thus, the films420, 421 are free to respond to acoustic waves incident upon them,resulting in induced voltages.

In the depicted embodiment, a PCB 422 is disposed in the upper cavity438 of the frame 418, and is in electrical contact with one or more ofthe electrodes of the first and second sensing elements 420, 421. Forexample, the PCB 422 can be in electrical contact with the anode andcathode of each of the sensing elements 420, 421. While otherconfigurations are possible, first and second ends 424, 426 of the firstsensing element 420 can generally extend underneath opposite sides ofthe PCB 422. A first end 428 of the second sensing element 421 extendsunderneath the PCB 422, while a second end 430 of the second sensingelement 421 extends over the opposing side of the PCB 422.

The upper side of the first ends 424, 428 of the first and secondsensing elements 420, 422 can include contacts (not shown) correspondingto both electrodes of the respective sensing elements 420, 421. Thesecontacts can be coupled to corresponding contacts on the underside ofthe PCB 422. One or more through holes or vias may be used to extend theelectrodes on the underside of the ends 424, 428 of the sensing elements420, 421 up to the upper side, enabling contact with appropriate PCB 422contacts. Example first and second sensing elements compatible with thearrangement of FIG. 4 are described with respect to FIGS. 5A-6B.Additionally, another example piezoelectric membranes including throughholes or vias are described below with respect to FIGS. 20A-20C.

While not shown for the purpose of clarity, in one embodiment, at leastone additional layer (not shown) can be disposed between the sensingelements 420, 421. The additional layer can include an adhesive thatadhesively couples the sensing elements 420, 421 together. This adhesivecoupling can help ensure that the sensing elements 420, 421 moveuniformly together in response to vibrations, reducing losses andimproving the response of the sensor. The adhesive coupling can also atleast partially maintain tension of one or more of the sensing elements420, 421.

The additional layer can further be configured to insulate the sensingelements 420, 421 from one another, preventing shorts, noise and/orother undesirable electrical behavior. For example, the additional layercan include a dielectric material. In an embodiment, the adhesivedescribed above acts as a dielectric material. Additional adhesivelayers are described below with respect to FIGS. 6A-6B, 19D-19E and6D-6E, for example.

The ends of the sensing elements 420, 422 may be configured to provideimproved sensor performance, reliability, etc. For example, theadditional layer may extend to the ends of one or more of the sensingelement 420, 422. In one embodiment, the additional layer is an adhesivelayer extending to the under side of the second end 430 of the secondsensing element 420, helping secure the connection between the secondsensing element 422 and the PCB 422. Moreover, in such embodiments, thesecond end 430 may be generally stretched across the top of the PCB 422,biasing one or more of the sensing elements 420, 421 in tension and thusproviding an improved piezoelectric response.

Depending on the embodiment, one or more of the ends of the sensingelements 420, 421 can also include a dielectric material. For example,in one embodiment, the underside of the second end 430 of the secondsensing element 421 includes a dielectric material, thereby insulatingthe second end 430 and the PCB 422. Additionally, the electrode coatingscan be configured to reduce the possibility of electrical shorts orother undesirable behavior. In one embodiment, for example, theelectrode coating on the underside of the second sensing element 421does not extend to the second end 430, thereby reducing the risk ofundesirable electrical contact between the second end 430 and the topsurface of the PCB 422. In another embodiment, a dielectric material isplaced on the underside of the PCB 422 instead of or in addition toproviding a dielectric material on the end of the sensing element 420 or421.

A variety of other configurations are possible for the arrangement ofthe sensing elements 420, 421. For example, in one embodiment, the endsof the sensing elements 420, 421 which are not connected to the PCB 422do not extend over or under the PCB 422. In another embodiment, each endof the sensing elements 420, 421 includes one electrode contact, and allfour ends are thus in electrical contact with corresponding contacts onthe PCB 422. This is in contrast with the arrangement described above,in which the upper side of the first ends 424, 428 each include bothanode and cathode electrode contacts for the respective sensing elements420, 421.

As discussed, and as with many of the embodiments described herein, thepiezoelectric films 420, 421 are shown in FIG. 4A spaced apart forclarity and ease of illustration. However, in addition to the additionallayers described above, the two piezoelectric films 420, 421 can beseparated by one or more mechanical supports, acoustic decouplers,shielding layers, or other layers or components. Additionally, any ofthese layers may be disposed between the frame 418 and the firstpiezoelectric film 420 and/or wrapped around the outside of the secondsensing element 421.

Shielding Using Multiple Sensing Elements

In certain embodiments, multiple sensing elements can be employed toform an electrical noise shielding barrier, providing electricalshielding. Moreover, using the sensing elements or portions thereof toform the barrier can simplify the design of the sensor, reducing costs.For example, one or more stacked sensing elements can be configured toelectrically shield the sensor. In some configurations, where thestacked sensing elements are piezoelectric films, the inner, facingelectrodes of the films in the stack are used to communicate voltagesignals generated by the piezoelectric elements to the sensing circuitryof the sensor (and/or monitor). The outer electrodes of the films in thestack can advantageously be configured to shield the inner electrodesfrom electrical noise. Generally, throughout the disclosure, the term“inner” refers to the sensing element surface and/or electrode coatingwhich is facing the other sensing element in the active region of thestack (e.g., across the acoustic cavity). Conversely, the term “outer”refers to the sensing element surface and/or electrode which is facingaway from the other sensing element in the active region of the stack.

The electrical noise shielding barrier can electrically shield theelectrical poles of the sensing element from external electrical noises.In some embodiments the outer portions of the sensing element form aFaraday cage or shield around the inner portions. Thus, the outerportions can distribute external electrical noise substantially equallyto the electrical poles of the piezoelectric sensing element. The shieldcan act to reduce the effect of noise on the sensing element fromsources such as external static electrical fields, electromagneticfields, and the like.

Using a second sensing element to form an electrical shielding barriercan also help to reduce costs by reducing the complexity involved inconstructing the sensor and reducing material costs. For example, suchembodiments may not include one or more shielding layers which arephysically separate from the sensing elements (e.g., copper shieldinglayers), reducing manufacturing costs associated with purchasing andhandling such components. However, certain aspects of shielding barriersformed from multiple sensing elements described herein are compatiblewith shielding barriers formed from separate layers and aspects thereof.Example shielding barriers including those formed from separateshielding layers are described with respect to FIGS. 2D-2E below andthroughout the '939 application, including, without limitation,paragraphs [0120]-[0146] and FIGS. 2D-2E of the '939 application whichare incorporated by reference herein.

FIG. 4B shows a partial cross-sectional schematic drawing of a portion440 of the first and second stacked piezoelectric films 420, 421 of FIG.4A. As shown, each of the first and second piezoelectric films 420, 421respectively include an anode 420 a, 421 a and a cathode 420 b, 421 b onopposing sides of the films 420, 421. In some embodiments, the films420, 421 include one of the piezoelectric films described with respectto FIGS. 2B-E or 3A-C, for example.

As shown, the films 420, 421 are disposed with respect to each other ina stacked configuration such that the cathode 420 b of the first film420 is facing the anode 421 a of the second film 421. Thus, these twoinner electrodes 420 b, 421 a of the stack are generally sandwichedbetween the anode 420 a of the first film 420 and the cathode 421 b ofthe second film 421, which form the outer electrodes of the stack. Theinner electrodes 420 b, 421 a can be operationally coupled to a sensingcircuit (e.g., a differential amplifier) in the manner shown in FIG.20B, advantageously providing improved signal-to-noise-ratio in someembodiments.

In addition, the outer electrodes 420 a, 421 b of the films 420, 421 canbe configured to form layers of an electrical noise shielding barrier,providing the additional benefit of electrically shielding the sensorfrom external electrical noises. The electrical noises shielded (or atleast partially shielded) can include electromagnetic interference (EMI)from various sources, such as 50 or 60 Hz (AC) noise, noise from othermedical devices, and so forth. In some embodiments for example, theouter electrodes 420 a, 421 b of the first and second films 420, 421form a barrier around the inner electrodes 420 b, 421 a of the first andsecond films 420, 421. Thus, a significant amount of external electricalnoise is not directly incident on the inner electrodes 420 b, 421 a. Theouter electrodes 420 a, 421 b can, for example, distribute at least aportion of the external electrical noise substantially equally to theinner electrodes 420 b, 421 a, which form the electrical poles of thesensor. For example, because the outer electrodes 420 a, 421 b may sharea common potential (e.g., ground), noise incident on either of the outerelectrodes 420 a, 421 b can be distributed equally to each electrode 420a, 421 b. The equally distributed noise can then be capacitively coupledto the inner electrodes 420 b, 421 a.

Thus, in certain embodiments, because the noise is equally distributed,the noise signal components on the inner electrodes 420 b, 421 a will besubstantially in phase. The physiological signal components can besubstantially out of phase, on the other hand, due to the differentialorientation of the inner electrodes 420 b, 421 a with respect to oneanother in some implementations. The noise signals can advantageously beremoved or substantially removed, such as through a common-moderejection technique as described herein. In certain embodiments, atleast some of the external electrical noise is shunted or otherwisedirected to ground instead of, or in addition to, being equallydistributed to the inner electrodes 420 b, 421 a.

A variety of alternative configurations are possible. For example, morethan two sensing elements (e.g., 2, 3, 4, 5 or more) may be arranged toprovide electrical shielding and/or improved signal-to-noise ratio insome embodiments. Moreover, the particular polarities of the sensingelements 420, 421 of FIG. 4 are not intended to be limiting. In anotherembodiment, one or more of the sensing elements 420, 421 are flipped.For example, the sensing elements 420, 421 are flipped such that theanode 420 a of the first sensing element 420 faces the cathode 421 b ofthe second sensing element 421.

Additionally, shielding barriers formed using stacked sensing elements420, 421 can provide improved coupling of bodily sounds to the sensor,improving sensor operation (e.g., sensor sensitivity, measurementreliability, etc.). Generally, portions of both the shielding barrierand the sensing element will tend to vibrate in response to the patientsounds. Thus, an uneven mechanical response between the shieldingbarrier and the sensing element may result in lost signal, affectingsensor performance. For example, shielding barriers including layersthat are physically separate from the sensing element can be, in somecases, relatively stiffer than the sensing element. This can limitmovement of the sensing element in response to vibrations, producing acorresponding limiting affect on sensor sensitivity. In contrast, whereelectrodes of the sensing elements are used as shielding layers, theshielding barrier and the sensing element are generally formed from thesame type material and integrally connected. Thus, the sensor may berelatively more responsive to vibrations, improving sensor operation.

Moreover, each of the outer electrode shield layers in the stackedconfiguration can be evenly spaced from the respective inner electrodesensor poles, particularly across the mechanically active portions ofthe sensor (e.g., across the frame cavity 436 of FIG. 4A). Thecapacitance between the shield layer and sensor pole on a first side ofthe sensing element stack can be very highly matched (e.g.,substantially equal to) with the capacitance between the shield layerand sensor pole on the opposing side of the stack. Thus, a stackedsensing element configuration can provide a more even distribution ofexternal electrical noise to the poles of the sensing element, improvingnoise rejection.

According to certain aspects, the physical configuration of theelectrodes of the first and second films 420, 421 can be tailored toprovide improved electrical shielding. For example, the outer electrodes420 b, 421 a can be plated using a material selected to provide enhancedshielding. Although other materials may be used, in one embodiment, theouter electrodes 420 b, 421 a are plated with silver ink. Moreover, incertain embodiments, the outer electrode coatings of the piezoelectricstack cover a greater portion of the surface area of the respectivepiezoelectric films than the inner electrode coatings. For example, theouter electrode coatings may cover a significantly larger portion of thesurface area of the respective piezoelectric films than the innerelectrode coatings. In certain embodiments, for example, the outerelectrodes generally envelope or surround the inner electrodes or asubstantial portion thereof when the films 420, 421 are in a stackedconfiguration. Thus, the amount of surface area of the inner electrodeswhich is exposed to electrical noise is reduced due to the mechanicaland/or electrical barrier created by the surrounding outer electrodes.

FIGS. 5A-5D illustrate example sensing elements 520, 521 havingelectrode coating configurations tailored for use in a stackedconfiguration. FIGS. 5A-5B show example first and second (e.g., innerand outer) surfaces 524, 526 of a first example acoustic sensing element520. FIGS. 5C-5D show example first and second (e.g., inner and outer)surfaces 528, 530 of a second acoustic sensing element 521. While thefilms 520, 521 are shown in an unfolded configuration for the ease ofillustration, the second sensing element 521 may be wrapped around thefirst sensing element 520 on a frame as shown in FIGS. 4A-4B. Thus, thesensing elements 520, 521 are also referred to as the interior andexterior sensing elements, respectively.

The interior sensing element 520 includes an anode electrode coating 520a on the outer surface 526 which extends via a through hole 532 to aportion on one end the end of the inner surface 524. The inner surface524 of the first sensing element 520 also includes a cathode coating 520b. The exterior sensing element 521 includes an anode electrode coating521 a on the inner surface 528 which extends via a through hole 534 to aportion on one end of the outer surface 530. The outer surface of theexterior sensing element 521 also includes a cathode electrode coating521 b.

As shown in FIG. 5B, the outer electrode surface of the first (interior)film 520 covers a substantially greater percentage of the surface areaof the outer surface 526 of the film 520 than do the inner electrodesurfaces on the opposing, inner surface 524 of the film 520, shown inFIG. 5A. For example, in the illustrated embodiment, the outer electrodecoating shown on FIG. 5B covers substantially the entire outer surface526 area of the film 520, while the electrode coatings on the innersurface 524 form a pair of generally rectangular strips covering only aportion of the inner surface 524 area of the film 520. Similarly, asshown in FIGS. 5C-D, the outer electrode coatings on the outer surface530 of the second (exterior) film 521 covers a substantially greatersurface area of the outer surface 530 of film 521 than the innerelectrode coating on the inner surface 528 of the film 521. For example,in certain embodiments, the electrode coating on the exterior surface ofone or more of the films 520, 521 covers at least 2 percent more of thefilm surface area than the do the interior electrodes. In otherembodiments, the exterior electrodes cover at least 1, 5, 10, 15 orgreater percent more of the exterior surface area than the do theinterior electrodes. Additionally, the exterior electrode can cover atleast 90 percent of the exterior film surface in some embodiments. Inother embodiments, the exterior electrode covers at least 70, 75, 80,85, 95 or more percent of the exterior film surface.

As described with respect to FIGS. 4A-4B, the through holes 532, 534facilitate electrical contact between the respective electrodes and oneor more components of the sensor (e.g., a PCB contact). Moreover, theelectrode which is extended to the opposing side through the at leastone through hole 540 can be electrically isolated from the otherelectrode on the respective film the by gaps 536, 538 in the electrodecoatings.

In such embodiments, where an electrode coating covers substantially theentire surface area of the piezoelectric film, or otherwise covers asignificantly larger portion of the surface area of the piezoelectricfilm than the electrode coating on the opposing side, the electrodecoating may be referred to as “flooded.” Thus, the configuration of FIG.5 generally includes un-flooded inner electrodes generally sandwichedbetween flooded outer electrodes. Such configurations can reduce surfacearea of the inner electrodes that is exposed to electrical noise,improving electrical shielding.

A wide variety of flooded electrode configurations are possible. Forexample, in some embodiments, the sizes and shapes of the electrodecoatings may differ from the illustrated embodiment. The relative sizesof the inner electrode coatings versus the outer electrode coatings canalso vary. For example, the inner electrode coatings are much smaller inrelation to the outer electrode coatings than is shown.

In some alternative embodiments, the outer and inner electrode coatingsare both flooded or otherwise cover about the same surface area, or theelectrode coating on the inner electrode coating covers more surfacearea than the outer electrode. Such embodiments may, in some cases,provide relatively less shielding than embodiments where the outerelectrode coatings cover more surface area than the inner electrodes,but nonetheless provide some significant amount of electrical shielding.

Example Sensor

FIGS. 6A-6B illustrate an exploded view of an example sensor 600configured to detect acoustic physiological sounds from the patientincorporating certain beneficial aspects described herein. For example,the sensor 600 provides improved SNR using multiple sensing elementsaccording to techniques described above with respect to FIGS. 2A-4B.Moreover, the sensor 600 includes a stacked, multiple sensing elementconfiguration providing enhanced shielding, compatible with thetechniques described above with respect to FIGS. 4A-5D.

The sensor 600 is generally attachable to a patient and can be coupledto a patient monitor. For example, the sensor 600 can be used with thesystem 10 of FIGS. 1A-1B. Additionally, the sensor 600 may be compatiblewith the sensor system 100 of FIG. 1C. For example, the sensor 600 maybe the sensor 101 of FIG. 1C, and can include an attachment mechanism(not shown) for attaching the sensor to a patient, such as theattachment subassembly 104 of FIG. 1C.

Referring to FIG. 6A, the sensor 600 of certain embodiments includes anacoustic coupler shell 602, a printed circuit board (PCB) 604, a frame606, first and second acoustic sensing elements 620, 621, and multipleadhesive layers 608, 610, 612. The coupler shell 602 houses the frame606, which is generally configured to support various components of thesensor 600 in an assembled state, including the PCB 604, sensingelements 620, 621, and adhesive layers 608, 610, 612. The sensingelements 620, 621 are piezoelectric films in the illustrated embodiment,although other types of sensing elements can be used.

The components of the sensor 600 can be assembled similarly to thesensor 415 of FIG. 4A. For example, the first piezoelectric film 620 iswrapped around a portion of the frame 606 and extends across an acousticcavity 614 (FIG. 6B) of the frame 606 in tension. When assembled, theadhesive portions 608, 610 are positioned between interior opposingsides of the first film 620 and corresponding sides of the sensor frame606, thereby adhering the first film 620 in place with respect to theframe 606.

The adhesive layer 612 is wrapped around the first sensing element 621,and the second sensing element 621 is in turn wrapped around theadhesive layer 612, generally forming a piezoelectric stack. Asdiscussed with respect to FIG. 4A, the active portions of the films 620,621 that extend across the acoustic cavity 614 are thus generally freeto move in response to received vibrations, enabling detection of aphysiological signal when the sensor 600 is attached to the patient. Incertain embodiments, the acoustic cavity 614 or a portion thereofextends all the way through the frame 606. For example, the cavity mayform one or more holes in the interior portion of the frame 606.

The PCB 604 is positioned in the cavity 616 (FIG. 6A) such that theunderside of the PCB 604 comes into contact with the regions 617, 618 ofthe second film 621 and the regions 622, 624 of the first film 620. Theflap 626 of the second film 621 rests on top of the PCB 604 in theillustrated embodiment, allowing electrical coupling of the firstsensing element 620 to the PCB 604 and associated circuitry.

The coupler shell 602 is generally configured to transmit vibrationsreceived from the patient to the films 620, 621 in the piezoelectricstack. The acoustic coupler 602 can include a lower protrusion or bump628 (FIG. 6B) configured to press against the patient's body when theacoustic sensor 600 is fastened into place on the patient. The acousticcoupler 602 can also include a protrusion 630 (FIG. 6A) designed to abutagainst the films 620, 621 and to bias them in tension across theacoustic cavity 614. The coupler shell 602 can be similar to any of theacoustic couplers described herein, such as those described below withrespect to FIGS. 19A-19E, 21, and 22A-22B.

Generally, the piezoelectric films 620, 621 can be any of thosedescribed herein. In the illustrated embodiment, for example, the films620, 621 are the piezoelectric films described in FIGS. 5A-5D havingflooded electrode surfaces 632, 644, respectively, which form the outersurfaces of the piezoelectric stack. Moreover, the films 620, 621include one or more vias or through holes extending an electrode fromone surface of the film 620, 621 to a corresponding region 622, 617 onthe opposing surface of the respective film 620, 621. As discussedabove, this configuration enables coupling of the four electrodes (e.g.,the anode and cathode for each film 620, 621) to the appropriatecontacts on the underside of the PCB 222.

For example, in one embodiment, the region 618 (FIG. 6A) of the floodedcathode coating on the outer surface of the second film 621 touches oneor more of the contacts 636 on the underside of the PCB 604 (FIG. 6B).Meanwhile, the through-holed region 617 (FIG. 6A) of the outer surfaceof the second film 621, which includes an anode coating, touches thecontact 638 on the underside of the PCB 604 (FIG. 6B). Regarding thefirst film 620, the region 624 (FIG. 6A) of the cathode coating on theinner surface touches one or more of the contacts 640 on the undersideof the PCB 604 (FIG. 6B). Meanwhile, the through-holed region 622 (FIG.6A) of the inner surface of the first film 620, which includes an anodecoating, touches one or more of the contacts 642 on the underside of thePCB 604 (FIG. 6B).

According to the above-described connection scheme, the films 620, 621can be coupled to circuitry (not shown) residing on the PCB 222 or othersystem component (e.g., the hub or monitor) to provide improved SNRand/or electrical shielding. For example, the electrodes of the films620, 621 can each be coupled to an input of an attenuation circuit(e.g., a differential amplifier) or ground (or other common potential)in the manner illustrated schematically with respect to FIG. 3B above.Specifically, although other connections schemes are possible, in oneembodiment, the contact 636 on the PCB 604 couples the flooded, outercathode of the second, exterior film 621 to ground, and the contact 642couples the outer, flooded anode of the first, interior film 620 toground. Moreover, the contacts 642 couple the inner, un-flooded anode ofthe second, exterior film 621 to a first (e.g., positive) terminal of adifference amplifier or other noise attenuation circuit. Finally, thecontacts 638 couple the un-flooded, inner cathode of the first, interiorfilm 620 to a second (e.g., negative) terminal of the differenceamplifier.

The frame 606 can include one or more pressure equalization pathways650. The pressure equalization pathways 650 provide an air communicationpathway between the lower acoustic cavity 614 and ambient air pressure.The pressure equalization pathways 650 allow the sensor's membrane(s) orfilm(s) 621, 622 to vibrate within the cavity 614 independent of skinelasticity or the force used to attach the sensor to a patient's skin.

Indeed, variability in skin elasticity or the force used to attach theacoustic sensor to the medical patient's skin can affect the volumeand/or air pressure within the cavity 614 defined by the sensingelements 621, 622 and frame 606. Variability in skin elasticity orattachment force can lead to variability in cavity resonance, which cancause unwanted variability in sensor 600 performance. For example, anacoustic sensor 600 that is attached to very elastic skin may provide adifferent output signal than an acoustic sensor 600 that is attached tofirmer or tighter skin. Similarly, an acoustic sensor 600 that isloosely attached to patient's skin may provide a different output signalthan an acoustic sensor 600 that is tightly attached to a patient'sskin.

To compensate for attachment variability, in one embodiment the acousticsensor frame 606 includes one or more pressure equalization pathways650. The pathways 650 provide an air-flow channel from the cavity 614 tothe ambient air pressure. By equalizing pressure within the cavity 614with ambient during sensing, variability in sensor performance may bereduced and/or eliminated. In some embodiments, the pressureequalization pathways 650 include one or more holes, notches, ports, orchannels that extend from within the sensor's cavity 614 to a locationin communication with ambient air pressure.

In one embodiment, the pressure equalization pathways 650 are providedon opposite sides of the frame 606 portion that defines an acousticcavity 614. Symmetrically arranging the pressure equalization pathways650 can further improve sensor 600 performance. In another embodimentthe pressure equalization pathways 650 are provided in portions of thesensor frame 606 which do not contact the sensor's sensing elements,membranes, and/or films 621, 622. By preventing contact between thepressure equalization pathways 650 and the sensor's sensing membrane,sensor 600 performance may be further improved.

In one embodiment, the sensor frame 606 includes one, two, three, four,or five pressure equalization pathways 650 on each of two opposite sidesof the sensor frame 606. In another embodiment, the sensor frame 606includes at least one pressure equalization pathway 650 on each of itssides. In one embodiment, each pressure equalization pathway 650 isformed as a notch. A frame 606 that includes notches as its pressureequalization pathways 650 may be easier to fabricate than a frame thatincludes other pressure equalization pathways 650 (e.g., holes). Forexample, when the frame 606 is made by molding plastic, creating notchesin the frame's 606 side wall requires less complicated tooling thanforming holes.

Aspects of some of the components of the sensor 600 are described ingreater detail herein with respect to other embodiments. For example,one or more of the coupling shell 602, PCB 604, frame 606, sensingelements 620, 621, adhesive layers 608, 610, 612, or portions or aspectsthereof are compatible with the corresponding components shown in FIGS.19A-23E and described in the accompanying text.

Noise Compensation Overview

Embodiments of systems generally including at least first and secondacoustic sensing elements and configured to provide noise compensationwill now be described with respect to FIGS. 7-18. As will be described,according to some aspects, one of the sensing elements is used as aphysiological signal sensing element, and another is used as a noisesensing element for generating a noise reference signal. The noisereference signal can be used to generate a physiological signal have areduced noise component according to a variety of techniques describedin further detail herein (e.g., adaptive filtering techniques).Moreover, according yet other embodiments, the sensing elements areselectively configurable for use as either physiological signal sensingelements or noise sensing elements, as desired, as described in furtherdetail herein.

According to various aspects, the multiple acoustic sensing elements canbe beneficially arranged in a variety of configurations. For example,the first and second sensing elements can be incorporated into the samesensor package, as shown in the embodiments illustrated in FIGS. 8 and10-15. In some embodiments, the first and second sensing elements areincluded in separate sensor packages, or can otherwise be strategicallypositioned at a variety of locations in the monitoring environment. Forexample, such sensors can be positioned at multiple locations on thepatient, as is shown in and described with respect to FIG. 9A. Moreover,one or more sensing elements can be positioned at the physiologicalmonitor or some other appropriate location in monitoring environment, asis disclosed in FIG. 9B and the accompanying text.

Generally speaking, the interfering noise signals described herein(e.g., with respect to FIGS. 7-18) can include any acoustic signal, andcan include vibrational, sonic, infrasonic, or ultrasonic waves. Suchsignals can be transmitted in gases, liquids and/or solids. For example,depending on the physiological signal being monitored, the interferingnoise can include patient sounds generated from physiological processes,such as breathing sounds, heart sounds, digestive sounds, combinationsof the same and the like. Interfering noise can further include speechsounds, snoring, coughing, gasping, etc., and can emanate from thepatient or other individuals in the monitoring environment. Furthersources of noise can also include humming or other acoustic noise comingfrom computers or other electronic equipment in the operatingenvironment, ambient traffic or airplane noise, combinations thereof andthe like.

Interfering noise can additionally emanate from one or more noisydevices that are coupled to the patient, such as medical devices thatare coupled to the patient during use. Examples of such devices caninclude, without limitation, powered surgical equipment (e.g.,electrosurgical tools for cauterizing, coagulating, welding, cutting,etc.), ventilation equipment (e.g., continuous positive airway pressure(CPAP) machines), nebulizers, combinations of the same and the like.

Particularly where a noise source is readily identifiable, the noisesensing element according to certain aspects may be positioned inphysical proximity to the noise source, so as to obtain a signalincluding a relatively clean noise reference signal, allowing forimproved noise compensation according to techniques described herein.Specific example cases are provided below with respect to FIGS. 9A-9B,for example.

According to yet other described embodiments, it can be expected thatthe components of their output signals resulting from one source (e.g.,the patient's body) will be generally similar while signal componentsfrom other sources (e.g., noise components) can be expected to havecertain dissimilarities (e.g., phase or time shift). In these cases, theoutput signals from the first and second acoustic sensing elements canbe advantageously combined in ways that accentuate commonalities betweenthe two signals while attenuating differences between the two outputsignals, or vice versa, producing a reduced noise output signal.

Moreover, while shown and described as first and second sensing elementswith respect to many of the embodiments described below, there may bemore than two (e.g., 3, 4, 5 or more) sensing elements in certainembodiments. Additionally, while described as individual sensingelements for the purposes of illustration, in certain embodiments one ormore of the first and second sensing elements each include multipleacoustic transducers or other types of sensing elements. In someembodiments, for example, the first and/or second sensing elements eachinclude at least two piezoelectric films arranged in a stackedconfiguration, wrapped around a support frame, as described above withrespect to FIGS. 3B-4B and 6A-6B.

FIG. 7 is a block diagram of an embodiment of an acoustic physiologicalmonitoring system 700 having noise compensation features. The noisecompensation features can be useful for reducing any deleterious effectof acoustic noise on the accuracy of physiological characteristicsdetermined using the monitoring system 700.

The acoustic physiological monitoring system 700 includes a firstacoustic sensing element 720 and a second acoustic sensing element 721.In some embodiments, these acoustic sensing elements are passivedevices. In some embodiments, the first acoustic sensing element 720 isused to produce a physiological signal 730 that is indicative of one ormore physiological sounds (e.g., sounds resulting from physiologicalprocesses) emanating from a patient's body. For example, the firstacoustic sensing element 720 may be used to produce a physiologicalsignal 730 that is indicative of a particular type of physiologicalsound, which is sometimes referred to herein as the target physiologicalsound. A variety of target physiological sounds are possible, includingbreathing sounds, heart sounds, digestive sounds, and the like. Forexample, the sensing elements 720, 721 can be piezoelectric films. Ingeneral, this physiological signal 730 can include unwanted noise as aresult of interfering noise in the patient's surroundings being pickedup by the first acoustic sensing element 720. The physiologicalcomponent and the noise component of the signal 730 can overlap in timeand/or frequency content. Devices for detecting primarily physiologicalsounds emanating from the patient's body are disclosed more fullyherein.

In some embodiments, the second acoustic sensing element 721 is used toproduce a noise signal that is substantially representative of, orotherwise meaningfully correlated with, any noise picked up by the firstacoustic sensing element 720. The noise signal 731 may not necessarilyduplicate the noise component of the physiological signal 730. Forexample, the signal strength of the noise in the two signals 730, 731can differ. Other differences between the noise signal 731 and the noisecomponent of the physiological signal 730 are also possible. However, itcan be advantageous for the second acoustic sensing element to bepositioned and designed such that the noise signal 731 has some degreeof commonality with the noise present in the physiological signal 730.In this way, the noise signal 731 can provide useful information tomeaningfully reduce, remove, filter, cancel, separate out, etc. thenoise from the physiological signal 730. Devices for detecting primarilynoise sounds are disclosed more fully herein.

In addition, the second acoustic sensing element 721 can also bepositioned and designed such that the noise signal 731 is substantiallyfree of the physiological sounds picked up by the first acoustic sensingelement 720, or such that such physiological sounds are aless-significant component of the noise signal 731 than they are of thephysiological signal 730. While illustrated as producing a noise signal731, in other embodiments discussed more fully herein the secondacoustic sensing element is positioned and designed to provide a secondphysiological signal rather than a noise reference signal. For example,like the first sensing element 720, the second acoustic sensing element721 may include both a significant physiological signal component and aninterfering noise component. In such embodiments, the first and secondphysiological signals can be combined in certain ways so as to reinforcethe physiological components of the two signals while reducing any noisecomponents that can exist in the two physiological components. In otherembodiments, this can be carried out using more than two acousticsensing elements.

In some embodiments, the physiological signal mixed with noise 730 andthe noise signal 731 are input to a processing unit 790. In someembodiments, the processing unit 790 includes a noise attenuator 740, asignal quality calculator 750, and a physiological characteristiccalculator 760. The processing unit 790 can be implemented as one ormore digital signal processors, one or more analog electric processingcomponents, combinations of the same or the like, etc.

In some embodiments, the noise attenuator 740 reduces the amount ofnoise present in the physiological signal 730 based on informationgleaned from the noise signal 731, as discussed in more detail herein.For example, the noise attenuator 740 can reduce the signal energy ofthe noise component of the physiological signal 730. Alternatively, orin addition, the noise attenuator 740 can reduce or remove a portion ofthe noise component of the physiological signal 730 over a particularfrequency range. In some embodiments, the processing unit 790 outputs aphysiological signal with reduced noise 741 using the noise attenuator740. The signal 741 can also be provided to other sub-blocks of theprocessing unit 790 (e.g., the physiological characteristic calculator760).

The signal quality calculator 750 is a device that is used to determine,for example, an objective indicator of the quality of the physiologicalinformation obtained from one or more acoustic sensing elements. Thiscan be done, for example, by comparing the physiological signal 730 withthe noise signal 731, as discussed further herein. The signal qualitycalculator 750 can also output an objective indicator of the degree ofconfidence in the accuracy of a physiological characteristic (e.g.,respiratory rate) determined based on the physiological informationcollected from one or more acoustic sensors. The signal qualitycalculator 750 can also output a binary confidence indicator thatselectively indicates low confidence and/or high confidence in theaccuracy of the physiological characteristic. The processing unit 790then outputs one or more signal quality indicators 751.

The physiological characteristic calculator 760 is used to determine,for example, one or more values or signals that are indicative of aphysiological characteristic of the patient. For example, thephysiological characteristic can be respiratory rate, expiratory flow,tidal volume, minute volume, apnea duration, breath sounds, riles,ronchi, stridor, and changes in breath sounds such as decreased volumeor change in airflow. In some embodiments, a physiologicalcharacteristic is calculated using a processing algorithm applied to thephysiological signal with reduced noise 741 that is outputted by thenoise attenuator 740.

The physiological signal with reduced noise 741, the signal qualityindicator 751, and the physiological characteristic indicator can beoutput to a display and/or speaker 780 to be viewed or heard by acaregiver. For example, in some embodiments, the physiological signalwith reduced noise 741 is converted back to an audible sound by way of aspeaker or other acoustic transducer so that it can be heard by a doctorand used for diagnosis of the patient. In some embodiments, the signalquality indicator 751 and the physiological characteristic indicator 761are displayed on a screen. This information can take the form of anumerical value, a plotted signal, an icon, etc.

Although both the noise attenuator 740 and the signal quality calculator750 are included in the example processing unit 790 shown, theprocessing unit 790 could include either the noise attenuator 740 or thesignal quality calculator 750 in some embodiments.

In various embodiments, the first and second acoustic sensing elements720, 721 can be either the same or different types of acoustic sensingelements. For example, in one embodiment, both of the sensing elementsare piezoelectric films such as any of the films described herein. Insuch a configuration, each of the sensing elements 720, 721 may behoused in a separate sensor packaging. As an example where differenttypes of sensing elements are used, the first sensing element 720 in oneembodiment is a piezoelectric film, while the second sensing element isa microphone, vibrational sensor or other type of acoustic pickupdevice. Such an embodiment is described with respect to FIG. 15 below.

Additionally, the sensing elements 720, 721 may be physically separatefrom one another. For example, the sensing elements 720, 721 can bephysically separated within a single wearable sensor package. In otherembodiments, the first sensing element 720 may be located on a wearablesensor package, such as any of those described herein, while the secondsensing element 721 may be located at some other location, such as, forexample, on a cable, hub, monitor, or in another wearable sensor packageat a different location on the patient, etc. Further embodiments ofsensors including physically separate sensing elements are discussedherein, with respect to FIGS. 8-9B, for example.

While embodiments described herein advantageously employ multiplesensing elements to achieve noise compensation, in certain embodiments,noise compensation is achieved using a single sensing element. Forexample, the sensing element may be coupled to the patient and thusproduce a signal including both physiological and noise components.However, in such embodiments, the noise reference signal may beextracted during periods when the physiological signal is inactive(e.g., in between patient breaths, heart beats, etc.). The extractedreference signal can then be used in accordance with techniquesdescribed herein to provide noise compensation.

FIG. 8 is a block diagram of an embodiment of an acoustic physiologicalmonitoring system 800 with a wearable acoustic sensor 815 that includesfirst and second acoustic sensing elements 820, 821. The first andsecond acoustic sensing elements 820, 821 are, for example, transducersfor converting sound waves into some other form of energy (e.g.,electrical voltage or current signals) to be processed, measured, etc.The first and second acoustic sensing elements 820, 821 can be packagedin a common housing as shown in FIG. 8, or in separate housings, asshown in FIG. 9A, described below. In some embodiments, the first andsecond acoustic sensing elements 820, 821 are both the same type ofacoustic transducer. For example, in some embodiments, the first andsecond acoustic sensing elements 820, 821 are both piezoelectric films.

Even in cases where the first and second acoustic sensing elements 820,821 are generally the same type of acoustic transducer, they need not beidentical. For example, in the case where both of the first and secondacoustic sensing elements 820, 821 are piezoelectric films, the materialproperties of the two films can be separately adapted based on knowncharacteristics of the aural signals they are intended to sense. Thefirst and second acoustic sensing elements 820, 821 can be made ofdifferent piezoelectric materials, they can have different shapes andthicknesses, they can have different support/mounting structures, andthey can have different packaging. For example, in a given application(e.g., a medical sensing application), system designers can haveforeknowledge regarding the characteristics of the sought-after acousticsignals.

As described herein, in some embodiments, the first acoustic sensingelement 820 is used to primarily sense physiological signals, while thesecond acoustic sensing element 821 is used primarily to sense noise. Insuch cases, the type of piezoelectric material, and its shape,thickness, its mounting and packaging, etc. can be adapted for each ofthe acoustic sensing elements 820, 821 based on unique characteristics(e.g., frequency range, amplitude, etc.) of the physiological signalsand the expected noise, respectively, if such unique characteristicsexist and are identifiable.

In other embodiments, it is advantageous for the properties (e.g.,material properties, mounting, packaging, etc.) of the first and secondacoustic sensing elements 820, 821 to be substantially similar or evenidentical. This can be the case, for example, where the acoustic signalsto be sensed by the two acoustic sensing elements 820, 821 have noimportant pre-identifiable differing characteristics.

It can also be advantageous for the first and second acoustic sensingelements 820, 821 to be substantially similar or even identical in termsof material properties, mounting, and packaging so that their signaloutputs will likewise have shared characteristics in response toexcitation of the acoustic sensing elements by a common source. This canbe the case where the outputs of the first and second acoustic sensingelements 820, 821 are to be combined using techniques for selecting orrejecting signal components from the two sensing element outputs basedon their common or distinguishing features. Examples of such techniquesare described in further detail herein.

In other embodiments, the first and second acoustic sensing elements820, 821 are different types of acoustic transducers. For example, thefirst and second acoustic sensing elements 820, 821 can be independentlyselected from a group including, but not limited to, piezoelectricacoustic transducers, condenser acoustic transducers, MEMS acoustictransducers, and electromagnetic induction acoustic transducers. Othertypes of acoustic transducers can also be used.

The first and second acoustic sensing elements 820, 821 can exhibitdirectionality or not. In cases where both of the first and secondacoustic sensing elements 820, 821 exhibit directionality, they can beaimed at a common location (e.g., the patient's skin) or a differentlocation (e.g., the first acoustic sensing element 820 could be aimed atthe patient's skin to detect physiological sounds, while the secondacoustic sensing element could be directed away from the patient's skinso as to detect ambient noise). In addition, in some embodiments, one ofthe acoustic sensing elements can exhibit directionality while the otherdoes not. For example, in some embodiments the first acoustic sensingelement 820 can exhibit directionality and be aimed at the patient'sskin for detecting physiological sounds, while the second acousticsensing element 821 does not exhibit directionality so as to detectnoise from all directions.

As described herein (e.g., with respect to acoustic sensor 201), theacoustic sensor 815 can include a cable 806, or other communicationlink, for communicating with a physiological monitor 807. For example,one or more connectors, hubs, or other cables may be included asdescribed herein. The acoustic sensor can also include one or moredevices (e.g., electrical circuits) for detecting, processing, andtransmitting the outputs from the first and second acoustic sensingelements 820, 821. The sensor can also include a fastener for fasteningthe sensor to the body of a patient. In some embodiments, the fasteneris specially adapted to attach to the patient's neck or chest region inorder to sense breathing sounds. The acoustic sensor 815 can alsoinclude other features described with respect to acoustic sensor 201.

In some embodiments, the acoustic sensor 815 is adapted to becommunicatively coupled with a separate physiological monitor 807 thatis not worn by the patient 801. (The physiological monitor 807 caninclude, for example, a display 880, a physiological characteristiccalculator 860, a noise attenuator 840, a speaker 881, and a signalquality calculator 850, as described herein.) Thus, in some embodiments,the first and second acoustic sensing elements 820, 821 are disposed onor in an acoustic sensor 815 that is adapted to be worn by the patient801, while the signal outputs from the first and second acoustic sensingelements 820, 821, which can include the raw signals directly from theacoustic sensing elements 820, 821 as well as processed signals derivedtherefrom, are transmitted to a separate physiological monitor 807 thatis not worn by the patient 801. In other embodiments, however, theacoustic sensor 815 and the physiological monitor 807 can both bewearable by the patient 801.

As discussed herein, in some embodiments the first acoustic sensingelement 820 is designed and used primarily to sense an acousticphysiological signal emanating from a patient's body, while the secondacoustic sensing element 821 is used primarily to sense the acousticnoise. The first acoustic sensing element 820 can, however, also detectacoustic noise. In this case, the noise signal from the second acousticsensing element 821 can be used as a noise reference to yieldinformation that can be used to reduce or remove the presence of theacoustic noise from the physiological signal at the output of the firstacoustic sensing element 820.

In cases where the second acoustic sensing element 821 is used toproduce a noise reference signal, it can be advantageous for the firstand second acoustic sensing elements 820, 821 to be designed andpositioned with respect to one another such that the noise referencesignal produced by the second acoustic sensing element 821 shares one ormore characteristics with the noise component of the physiologicalsignal output by the first acoustic sensing element. For example, thenoise reference signal can be meaningfully correlated with the noisecomponent of the physiological signal. In some embodiments, the noisereference signal from the second acoustic sensing element 821 and thenoise component of the physiological signal from the first acousticsensing element 820 are related by, for example, a scalar factor, a timeshift, a phase shift, or combinations of the same. Other relationshipsbetween the noise reference signal and the noise component of thephysiological signal are also possible.

In some embodiments, clinically meaningful correlation between the noisereference signal and the noise component of the physiological signal isachieved, at least in part, by placing the first and second acousticsensing elements 820, 821 in proximity to one another. For example, asillustrated in FIG. 8, the first and second acoustic sensing elements820, 821 can be commonly located on a wearable acoustic sensor 815.Disposing the first and second acoustic sensing elements 820, 821 inproximity to one another can improve correlation between the noisereference signal and the noise component of the physiological signal byreducing differences in, for example, the amplitude, frequency content,and phase between the noise sensed at the first acoustic sensing element820 as compared to the noise sensed at the second acoustic sensingelement 821.

The physical distance between the first and second acoustic sensingelements 820, 821 can vary from embodiment to embodiment depending upon,for example, the expected frequency content of the noise, the presenceof acoustically dispersive materials, acoustic reflectors or absorbers,or the like, that are located, for example, between the two sensingelements. For example, a physiological monitoring system 800 operated inan environment with relatively lower frequency noise (e.g., ambientnoise) can be able to tolerate larger physical distances between thefirst and second acoustic sensing elements since such distances will besmaller relative to the wavelength of the noise than in the case ofnoise with higher frequency content. Thus, even despite a relativelylarger physical separation between the first and second acoustic sensingelements, the noise sensed by the second acoustic sensing element canstill be reasonably indicative of, or related to, the noise sensed bythe first acoustic sensing element.

In some embodiments, the actual tolerable physical distance between thefirst and second acoustic sensing elements 820, 821 can depend upon theparticular application and/or noise-reducing requirements imposed by theapplication. In some embodiments, the first and second acoustic sensingelements 820, 821 can be physically disposed in close enough proximityto one another such that an noise reference signal detected by thesecond acoustic sensing element 821 contains a sufficient amount ofinformation regarding the noise component of the physiological signaldetected by the first acoustic sensing element 820 so as to provide aclinically significant reduction in the noise component of thephysiological signal. This can be manifested, for example, by aclinically significant improvement in the accuracy of a physiologicalcharacteristic (e.g., respiratory rate) determined by the physiologicalmonitoring system from a noise-reduced version of the physiologicalsignal detected by the first acoustic sensing element 820.

In some embodiments, the first and second acoustic sensing elements arephysically located within a 1 m radius of one another. In someembodiments the first and second acoustic sensing elements arephysically located within a 0.1 m radius of one another. In someembodiments the first and second acoustic sensing elements arephysically located within a 0.01 m radius of one another. In someembodiments the first and second acoustic sensing elements arephysically located within a 0.001 m radius of one another.

In some embodiments, the first and second sensing elements 820, 821 canbe disposed in separate sensor packages or otherwise be disposed atdifferent locations throughout the operating environment. For example,FIG. 9A is a block diagram of an embodiment of an acoustic physiologicalmonitoring system 900 with first and second acoustic sensing elements920, 921 disposed in or otherwise being associated with separate firstand second sensors 916, 917. While shown as being coupled to thephysiological monitor 907 via a single communication link 906, aseparate communication link 906 may be used for each sensor 916, 917 incertain embodiments. In some embodiments, each communication link 906includes one or more cables, hubs, and/or connectors as describedherein. FIG. 9B is a block diagram including a first sensing element 920disposed on a patient and a second sensing elements 920, 921 disposed ona physiological monitor 907.

Referring to FIG. 9A, the first and second sensors 816, 817 can bepositioned at a variety of locations on the patient 901. For example, incertain embodiments, one or both of the sensing elements 920, 921 (andtheir associated sensors 916, 917) can be positioned on or aroundsources of sounds generated by physiological processes. Such areas caninclude those associated respiratory or vocal sounds including forexample, the throat, back of the neck, mouth, or some other portion ofthe head or neck, on the back or chest around the lungs, combinations ofthe same and the like. Other sensing element locations can include thosegenerally associated with heart sounds, such as on the chest around theheart, on the throat, on the wrist, etc. Yet other locations can includethose typically associated with digestive sounds such as near thestomach or on some other portion of the abdomen. Moreover, while theabove examples are provided for the purposes of illustration, dependingon the application, the sensors 916, 917 can additionally be positionedat generally any location on the patient's body 901 including, forexample, a hand, finger, arm, foot, leg, etc.

FIG. 9C illustrates an example system 990 including dual acousticsensors 991, 992 applied to a patient's 993 throat and chest,respectively. FIG. 9D illustrates a second example where sensors 994,995 are applied to different regions of a patient's 996 chest. The dualacoustic sensors 991, 992, 994, 995 can be coupled to a physiologicalmonitor 997 via a hub and a plurality of cables, as shown. The sensors991, 992, 994, 995, monitor 997, cables, hub, etc., can be any of thosedescribed herein or incorporated by reference, or can be some otheracoustic sensors. Where multiple sensors are attached to the patient orare otherwise spatially separated throughout the operating environment,such an arrangement may be referred to as a stereo monitoringenvironment that allows for stereo body sound monitoring.

The sensing elements 920, 921 and, where present, associated sensorpackages, can additionally be positioned at one or more locations in theoperating environment not on the patient's body. For example, FIG. 9B isa block diagram of an embodiment of an acoustic physiological monitoringsystem 902 with a wearable acoustic sensor 915 that includes a firstacoustic sensing element 920, and a physiological monitor unit 907 thatincludes a second acoustic sensing element 921. The physiologicalmonitor unit 907 is adapted to be communicatively coupled with thewearable acoustic sensor 915 via, for example, a cable 906. In someembodiments, the physiological monitor unit 907 is a non-wearable unitwith one or more devices for processing signal outputs from the firstand second acoustic sensing elements 920, 921. The physiologicalmonitoring system 902 of FIG. 9B is similar to the physiologicalmonitoring systems 800, 900 except that the second acoustic sensingelement 921 is physically located at the non-wearable physiologicalmonitor 907 instead of at the wearable acoustic sensor 915.

While shown on the monitor 907, the second sensing element 921 can bepositioned at a variety of other locations. For example, in cases wherethe physiological monitor 907 and the acoustic sensor 915 arecommunicatively coupled using a physical cable 906, the cable 906 can beuseful in placing a limit on the distance between the first and secondacoustic sensing elements 920, 921 to ensure that they remain in closeenough proximity with one another to provide for meaningful noisereduction for a given medical sensing application. In other embodiments,the second acoustic sensing element 921 can be at any intermediatelocation between the monitor and the sensor, such as on or in the cable906, a connector, or a hub (not shown) such as the hub 120 of FIG. 1C,or generally at any separate location independent of the physiologicalmonitor 907 or the acoustic sensor 915. Where the second sensing element921 is used to generate a noise reference, positioning the secondsensing element 921 on or in the monitor 907, hub, or at anotherintermediate location, rather than on the sensor 915 can advantageouslyreduce the wiring overhead in the system. On the other hand, it can bebeneficial to locate the second sensing element 921 near the firstsensing element 920 so as to generate a noise reference signal that issubstantially correlated with the noise component of the signal detectedby the first sensing element 920. Thus, in certain cases, a trade offgenerally exists between locating the second sensing element 921 inproximity to the first sensing element 920 to improve noise rejection onthe one hand, and locating the second sensing element remote from thefirst sensing element 920 to reduce wiring overhead on the other. Thus,in circumstances, locating the second sensing element 921 at the hub orat another intermediate location between the monitor 907 and the firstsensing element 920 provides the desired balance between reduced wiringoverhead and adequate noise rejection.

As mentioned, where a noise source is readily identifiable, the secondsensing element 921 can be positioned in physical proximity to the noisesource. In this manner, the second sensing element 921 can be used toproduce a signal including a relatively clean noise reference signal,allowing for improved noise compensation. Such noise sources can bethose generating any of the interfering noise described herein such asnon-target physiological sounds emanating from the patient (e.g., heart,breathing or digestive sounds), ambient noise (e.g., traffic, ambientspeech sounds, computer humming, and the like), or vibrations or othernoise emanating from skin-coupled devices (e.g., electrosurgicaldevices, CPAP machines, nebulizers, etc.).

Several example scenarios incorporating multiple sensing elements 920,921 strategically located at separate locations in the operatingenvironment will now be described. These examples are provided for thepurposes of illustration, and are not intended to be limiting. As afirst illustrative example, referring to FIG. 9A, the first sensor 916is a physiological signal sensor and is positioned on or around a sourceof breathing sounds (e.g., the neck), while the second sensor 917 is anoise sensor and is positioned on or around the heart to detect heartsounds and/or other noise components. Thus, the signal from the secondsensor 917 can be used to cancel or otherwise attenuate any residualheart sounds (and/or ambient or other noise) that may bleed into thesignal produced by the first sensor 916.

In another example scenario, a CPAP machine or other medical device iscoupled to the patient. The first sensor 916 is a physiological signalsensor positioned on the patient's heart to detect heart sounds, and thesecond sensor 917 is a noise sensor positioned on the CPAP machine orother medical device. Thus, the signal produced by the second sensor 917can be used to cancel any residual noise from the CPAP machine (and/orambient or other noise) that bleeds into the signal detected by thefirst sensor 916.

In yet another illustrative example, the first sensor 916 is aphysiological signal sensor positioned to detect breathing sounds, andthe second sensor 917 is a noise sensor positioned on the patient near aplanned electrosurgical site (or on an electrosurgical device itself).The second sensor 917 can be used in such a situation to cancel noisegenerated by the electrosurgical device (and/or ambient or other noise)that bleeds into the signal detected by the first sensor 916.

Selective Configuration of Multiple Sensing Elements

Depending on the desired application, the multiple sensing elements canbe selectively configured in a plurality of modes. For example,referring still to FIGS. 9A-9B, the sensing elements 920, 921 can beconfigured as either physiological signal sensors or noise sensors insome embodiments. In addition to physiological sensing and noise modes,the sensing elements can be configured in a variety of other modes. Forexample, in one embodiment, one or more of the sensing elements 920, 921is configurable in an auscultation mode. For example, the sensingelements 920, 921 can be configured in a listening mode in which anoperator can generally continuously listen to audio output indicative ofpatient bodily or voice sounds. In yet another embodiment, the sensingelements 920, 921 can be configured to sense and process ultrasonicsignals (e.g., for ultrasonic imaging). Examples of sensors capable ofvarious types of audio output, ultrasonic sensing, and other compatiblefunctionality are provided in U.S. patent application Ser. No.12/905,036, entitled PHYSIOLOGICAL ACOUSTIC MONITORING SYSTEM, filed onOct. 14, 2010, incorporated by reference herein in its entirety.

As one example, the first sensor 916 is positioned on or around a sourceof breathing sounds (e.g., on the throat), while the second sensor 917is positioned on or around the heart to detect heart sounds. In a firstmode, the first sensor 916 is configured in a physiological sensing modeand the second sensor 917 is configured in a noise sensing mode, whilein a second mode, the roles of the sensors are generally switched. Inthis manner, breathing sounds are monitored and the effect of heartsounds (and/or other noise) is reduced according to noise cancellingtechniques described herein. Moreover, in the second mode, heart soundsare monitored, and the effect of any residual breathing sounds (and/orother noise) is reduced. Thus, according to such techniques, a user canflexibly and efficiently switch between monitoring reduced noiseversions of a wide variety of physiological signals.

Moreover, the sensing elements can be configured for use in more thanone mode at a time in certain embodiments. For example, each of thesensing elements 920, 921 can be configured simultaneously as bothphysiological signal sensing elements and noise sensing elements. In theabove example scenario, the first sensing element 920 can be used tomonitor breathing sounds and also generally simultaneously provide anoise reference to the second sensing element 921. Conversely, thesecond sensing element 921 can be used to monitor heart sounds and alsogenerally simultaneously provide a noise reference to the first sensingelement 920. While other modes are possible, in various embodiments, thesensing elements 920, 921 can be configured generally simultaneously fortwo or more of physiological signal sensing, noise sensing,auscultation, and ultrasonic sensing.

The configuration of the sensing elements 920, 921 may be manuallyselectable by a user, or can be automatically configurable by thesystem. For example, one or more user-actuatable inputs (e.g., buttons,switches, keypad inputs, etc.) may be provided to the user for settingthe sensing element 920, 921 modes. Such inputs may be located on themonitor 907, in proximity to the sensing elements 920, 921 themselves,such as on the respective sensor packaging, or at some other appropriatelocation.

Moreover, the modes of the sensing elements 920, 921 can be configurableeither as a group or individually in various embodiments. For example,referring to the above example where the first sensing element 920 ispositioned to detect breathing sounds and a second sensing element 921is positioned to detect heart sounds, the system may allow the user toselect either of a breathing sound monitoring mode or a heart soundmonitoring mode. Based on the selection, the system will appropriatelyautomatically configure each sensing element 920, 921 mode. In anotherembodiment, the user sets each of the respective sensing element 920,921 modes separately.

Where multiple sensing elements are present and are configured orselectively configurable for use as noise sensing elements, the systemaccording to some embodiments automatically selects which sensingelement or group thereof to use in the noise cancellation algorithm.Moreover, the outputs from multiple noise sensing elements or a selectedcombination thereof can be combined so as to provide improved noiserejection.

As one example, a first sensing element 920 is disposed on a wearableacoustic sensor 915 positioned on the patient's neck and is configuredto receive a signal including physiological signal components and noisecomponents. Second, third and fourth acoustic sensing elements aredisposed on the cable, at the hub, and in the monitor, respectively, andare configured to receive noise signals.

In such embodiments, the physiological monitor 907 or other systemcomponent can generally use signals received from at least one of thenoise acoustic sensing elements to perform noise reduction. For example,in the above example, each of the signals from the second, third andfourth sensing elements can be combined or otherwise used to performnoise compensation. In other cases, only a subset of one or more of thesignals may be used as desired.

The system 900 can allow for manual selection of the noise acousticsensing element(s) to use during monitoring, or can alternativelyautomatically select which of the noise acoustic sensors (e.g., thesecond third, or fourth sensing elements or a combination thereof) touse. Automatic selection can be performed in a variety of ways.

For example, in one embodiment, the system 900 evaluates the signalsfrom each of the noise acoustic sensors, such as by assessing themagnitude or quality of the respective noise signals, and selects one ormore of the signals to use based on the evaluation. For example, in someembodiments, the noise sensing element or combination of noise sensingelements that provides one or more of the highest amplitude noisereference signal or the cleanest noise reference signal is selected. Inanother embodiment, the system 900 assesses the degree of noisecompensation achieved using the different noise acoustic sensingelements and/or combinations thereof, and selects the noise acousticsensing element or combination thereof that provides the highest (orotherwise desirable) level of noise compensation to use duringmonitoring.

Noise Compensation Using Signal or Noise Correlation Between SensingElements

As described, it can be advantageous in certain embodiments for thefirst and second acoustic sensing elements to be substantially similaror even identical in terms of material properties, mounting, andpackaging so that their signal outputs will likewise have sharedcharacteristics in response to excitation of the acoustic sensingelements by a common source. This can be the case where the outputs ofthe first and second acoustic sensing elements are to be combined usingtechniques for selecting or rejecting signal components from the twosensing element outputs based on their common or distinguishingfeatures.

For example, referring to FIGS. 9A-9B for the purposes of illustration,in some applications it can be expected that, owing to similarities inthe design and placement of the first and second acoustic sensingelements 920, 921 or other factors, the components of their outputsignals resulting from a common source (e.g., the patient's body) willbe generally similar while signal components from other sources (e.g.,noise components) can be expected to have certain dissimilarities (e.g.,phase or time shift). In these cases, the output signals from the firstand second acoustic sensing elements 920, 921 can be combined in waysthat accentuate commonalities between the two signals while attenuatingdifferences between the two output signals.

In one example scenario, referring to FIG. 9A, the first and secondacoustic sensing elements 920, 921 are substantially the same type andare included in separate sensor packages each placed on the patient. Asdescribed, the physiological signal components produced by the sensingelements 920, 921 are substantially correlated with respect to oneanother. In some cases, the correlation can be enhanced via strategicplacement of the sensing elements 920, 921 with respect to one another.For example, the sensor packages can be placed generally symmetricallyabout the signal source (e.g., the throat or chest). In contrast, thenoise signal components produced by the sensing elements 920, 921 aresubstantially uncorrelated with respect to one another.

In such a scenario, the components can be uncorrelated for a variety ofreasons. For example, noise signals emanating from external sources mayreflect off of the skin or sensor package before reaching the respectivesensing element 920, 921. The signal may also propagate through aportion of the sensor package before reaching the respective sensingelement 920, 921, causing additional distortions. Moreover, the degreeand quality of distortion in the noise signal received by the sensingelements 920, 921 can differ significantly between the sensing elements920, 921. For example, in addition to other possible reasons, thevariation in distortion can be caused by a variation in the respectiveangle of arrival of the noise signal at each of the sensor packages.This can be due to the difference in the orientation of the noise sourcefrom one sensor package to another.

The output signals from the first and second acoustic sensing elements920, 921 in such a scenario can be combined to accentuate the correlatedphysiological signal components and attenuate the uncorrelated noisecomponents between the two output signals. For example, while a varietyof techniques can be used, the outputs from the sensing elements aresummed together in one embodiment. The correlated components will tendto additively combine, while the uncorrelated components will not,resulting in an overall improved SNR. In other embodiments, more thantwo (e.g., three, four, five or more) sensing elements 820, 821 areused.

In some other embodiments, certain noise components (e.g., ambient noisecomponents) of the signals produced by the first and second sensingelements 920, 921 may be correlated, while the physiological signalcomponents may be uncorrelated. In such cases, additional appropriatetechniques can be used to generate a reduced noise signal. Examples ofsuch techniques, including cross-correlation, are described in U.S.application Ser. No. 12/904,789, entitled ACOUSTIC RESPIRATORYMONITORING SYSTEMS AND METHODS, filed on Oct. 14, 2010, the entirety ofwhich is incorporated by reference herein.

Additional Noise Compensation Embodiments

FIG. 10 is a block diagram of an embodiment of an acoustic sensor 1015that includes a physiological signal acoustic sensing element 1020 withan acoustic coupler 1014 for acoustically coupling it to a patient'sbody, and a noise acoustic sensing element 1021. In some embodiments,the acoustic coupler 1014 is any device or structure, made using anymaterial, that effectively enhances the transmission of acoustic signalsfrom a patient's body to the physiological signal acoustic sensingelement 1020. In the case where the physiological signal acousticsensing element 1020 is a piezoelectric film, the acoustic coupler 1014can be a mechanical structure in contact with both the patient's skin1001 and the acoustic sensing element 1020 so as to transmit vibrationsfrom the patient's body to the physiological signal acoustic sensingelement. The acoustic coupler 1014 can be, for example, similar to theacoustic coupler 214 described herein. Other acoustic couplers can alsobe used. The acoustic sensing elements 1020, 1021 and the acousticcoupler 1014 can be physically supported in a desired spatialrelationship with respect to one another using, for example, a suitableframe.

The acoustic coupler 1014 provides an amount of acoustic couplingbetween the physiological signal acoustic sensing element 1020 and thepatient 1001 that is greater than the amount of acoustic coupling thatcan exist between the noise acoustic sensing element 1021 and thepatient. This increased amount of acoustic coupling is illustrated inFIG. 10 by solid double arrows. Of course, the physiological signal fromthe patient's body 1001 can also be picked up by the noise acousticsensing element 1021, just as noise can be picked up by both of theacoustic sensing elements 1020, 1021.

However, the strength of the physiological signal present in the outputof the noise acoustic sensing element 1021 will typically be less thanthe strength of the physiological signal present in the output of thephysiological signal acoustic sensing element 1020, as a result of thelack of an acoustic coupler between the patient's body 1001 and thenoise acoustic sensing element 1021. This is illustrated in FIG. 10 bythe dashed double arrows between the patient's skin 1001 and the noiseacoustic sensing element 1021. For example, in some embodiments, thestrength of the physiological signal in the output of the noise acousticsensing element 1021 is less than 50% of the strength of thephysiological signal in the output of the physiological signal acousticsensing element 1020. In some embodiments, the signal strength of thephysiological signal at the output of the noise acoustic sensing element1021 is less than 25%, or less than 10%, or less than 5%, of itsstrength at the output of the physiological signal acoustic sensingelement 1020.

In some embodiments, it is advantageous for the strength of thephysiological signal in the output of the noise acoustic sensing element1021 to be significantly less than the strength of the physiologicalsignal in the output of the physiological signal acoustic sensingelement 1020. In this way, the output of the noise acoustic sensingelement 1021 can be effectively used as a noise reference signal toprovide useful information for reducing the amount of noise present inthe output of the physiological signal acoustic sensing element 1020.

While in some embodiments it is advantageous for the two acousticsensing elements 1020, 1021 to be in close proximity so as to improvethe degree of correlation between the noise picked up by each acousticsensing element, it can be likewise advantageous for the noise acousticsensing element 1021 to be located further away from the patient's body1001 to reduce the strength of the physiological signal picked up by thenoise acoustic sensing element 1021. In some cases, these two designgoals can work in opposition to one another. However, in someembodiments, both advantages can be had by the addition of one or moreacoustic decouplers or isolators to the acoustic sensor.

FIG. 11 is a block diagram of an embodiment of an acoustic sensor 1115that includes a physiological signal acoustic sensing element 1120 withan acoustic coupler 1114 for increasing acoustic coupling between it anda patient's body, and a noise acoustic sensing element 1121 with anacoustic decoupler 1116 for decreasing acoustic coupling between it andthe patient's body 1101. The acoustic decoupler 1116 reduces further theamount of physiological sounds from the patient's body that is picked upby the noise acoustic sensing element 1121. Acoustic decoupling caninclude, for example, complete acoustic isolation or substantialacoustic isolation of the sensing element 1121 from the patient's skin1101. Thus, in certain embodiments, the acoustic decoupler 1116 canreduce sounds from being transmitted from the patient's skin 1101 to thesensing element 1121, or prevent the transmission of these soundsentirely.

This can be advantageous since the acoustic decoupler 1116 can providefor a higher degree of certainty that any similarities or correlationbetween the output of the noise acoustic sensing element 1121 and theoutput of the physiological signal acoustic sensing element 1120 aremore likely to be indicative of the acoustic noise than the targetphysiological sounds. This can, in turn, allow a noise attenuator deviceto more accurately or fully reduce the strength of the acoustic noisecomponent from the output of the physiological signal acoustic sensingelement 1120.

The acoustic decoupler 1116 can be any device or structure, made usingany material, that can effectively acoustically isolate differentcomponents. For example, the acoustic decoupler 1116 can be a device orstructure that is known to effectively reflect or absorb acoustic waves.In some embodiments, the acoustic sensor 1115 also includes one or moreadditional acoustic decouplers. For example, an acoustic decoupler 1117can be physically positioned between the physiological signal acousticsensing element 1120 and any expected source of noise, thereby reducingthe amount of noise picked up by the physiological signal acousticsensing element. The acoustic sensing elements 1120, 1121 and anyacoustic decouplers 1116, 1117 can be physically supported in a desiredspatial relationship with respect to one another using, for example, asuitable frame.

FIG. 12 is a cross-sectional schematic drawing of an embodiment of anacoustic sensor 1215 that includes a physiological signal acousticsensing element 1220 and a noise acoustic sensing element 1221. A frame1218 supports the two acoustic sensing elements 1220, 1221. In someembodiments, the frame 1218 is similar to the frame 218 describedherein. For example, the frame 1218 can provide an upper cavity 1230 anda lower cavity 1236. The lower cavity 1236 can be used to form anacoustic cavity for an acoustic sensing element, while the upper cavity1230 can be used to house printed circuit boards and electricalcomponents.

As discussed herein, in some embodiments, the two acoustic sensingelements 1220, 1221 are piezoelectric films, for example, similar tothose illustrated in FIGS. 3A-3C. Each of the piezoelectric films caninclude electrical poles across which a voltage is induced by acousticwaves in the piezoelectric films, as described herein. In theillustrated embodiment, the physiological signal acoustic sensingelement 1220 is a piezoelectric film wrapped around a portion of theframe 1218 and extending across the lower cavity 1236 in tension. Thus,the lower cavity 1236 serves as an acoustic cavity, and thepiezoelectric film 1220 stretched in tension across the acoustic cavity1236 is free to respond to acoustic waves incident upon it.

In some embodiments, the noise acoustic sensing element 1221 is likewisea piezoelectric film wrapped around a portion of the frame 1218. Thepiezoelectric film 1221 can be bonded to the frame 1218 using, forexample, an adhesive layer. In this way, the piezoelectric film 1221 canvibrate in conjunction with the frame 1218 in response to acoustic wavesthat are incident upon it.

The piezoelectric films 1220, 1221 are shown in FIG. 12 spaced apart forclarity and ease of illustration. It should also be understood that, insome embodiments, other layers can be present, such as any of theadditional layers described above. The two piezoelectric films 1220,1221 can be separated by one or more adhesive layers, electricalinsulators, mechanical supports, acoustic decouplers, etc.

The acoustic sensor 1215 also includes an acoustic coupler 1214. In someembodiments, the acoustic coupler 1214 is similar to the acousticcoupler 214 described herein. The acoustic coupler 214 can include alower protrusion or bump configured to press against the skin 1201 of apatient when the acoustic sensor is fastened into place on the patient.The acoustic coupler 1214 can also include a protrusion 1212 designed toabut against the physiological signal acoustic sensing element 1220 andto bias it in tension across the acoustic cavity 1236. The acousticcoupler 1214 can also include sidewalls 1213 that extend upward andenclose at least a portion of the frame 1218.

For clarity of illustration, not all of the components of the acousticsensor 1215 are illustrated. The frame 1218, the piezoelectric film1220, and the acoustic coupler 1214 can all include any of the featuresdescribed herein or illustrated with respect to FIGS. 2A-6E. Inaddition, the acoustic sensor 1215 can include any of the featuresdisclosed or illustrated with respect to the same figures, includingbonding layers, electrical shielding layers, sealing layers, etc. Theacoustic sensor 1215 can also include electrical components (e.g., avoltage detector circuit to detect the electrical voltages inducedacross the poles of each of the piezoelectric films 1220, 1221), printedcircuit boards, cables, patient fasteners, and other features disclosedherein.

While FIG. 12 illustrates that the two acoustic sensing elements 1220,1221 are layered one on top of the other, they could instead be disposedwith other layouts. For example, the two acoustic sensing elements 1220,1221 could be supported by the frame 1218 side-by-side. In addition,while both acoustic sensing elements 1220, 1221 are illustrated as beingsupported by a common frame 1218 inside a common housing, they couldinstead each be supported by a separate frame and/or have separatehousings. Of course, the frame 1218 could also take many differentshapes than the one illustrated.

FIG. 13 is a cross-sectional schematic drawing of another embodiment ofan acoustic sensor 1315 that includes a physiological signal acousticsensing element 1320 and a noise acoustic sensing element 1321. Theacoustic sensing elements 1320, 1321 and the acoustic coupler 1314 areas already described with respect to FIG. 12. The frame 1318, however,includes another cavity 1332 in addition to the upper cavity 1330 andthe lower cavity 1336. As illustrated, the noise acoustic sensingelement 1321, a piezoelectric film, stretches across the cavity 1332 intension to form an acoustic cavity for the noise acoustic sensingelement. The presence of the acoustic cavity 1332 allows the noiseacoustic sensing element 1321 greater freedom to vibrate in response toacoustic waves that are incident upon it.

As illustrated in FIG. 13, the acoustic cavity 1332 for the noiseacoustic sensing element 1321 can be provided as a depression inside thefloor of the acoustic cavity 1336 for the physiological signal acousticsensing element 1320. The acoustic cavity 1332 could also be formed inone or both of the sidewalls of the acoustic cavity 1336. Alternatively,the acoustic cavity 1332 could be formed in some other portion of theframe 1318 independent of the acoustic cavity 1336 for the physiologicalsignal acoustic sensing element 1320. In some embodiments, all or aportion of the upper cavity 1330 provided by the frame 1318 can serve asan acoustic cavity for the noise acoustic sensing element 1321. Forexample, the noise acoustic sensing element 1321 could stretch acrossthe upper cavity 1330 in tension. Many other multiple-acoustic-cavitylayouts are also possible.

FIG. 14 is a cross-sectional schematic drawing of another embodiment ofan acoustic sensor 1415 that includes a physiological signal acousticsensing element 1420 and a noise acoustic sensing element 1421. Onceagain, in this embodiment, the physiological signal acoustic sensingelement is a piezoelectric film 1420. An acoustic coupler 1414acoustically couples the piezoelectric film 1420 to the patient's body1401. The noise acoustic sensing element 1421 is likewise apiezoelectric film. However, the position of the noise acoustic sensingelement 1421 differs from that of the embodiment illustrated in, forexample, FIG. 13 in that the piezoelectric film 1421 shares the acousticcavity 1436. In the embodiment of FIG. 14, the two piezoelectric films1420, 1421 both extend over the acoustic cavity 1436 adjacent to oneanother. This is shown in the bottom view 1450 of the two piezoelectricfilms 1420, 1421. Other physical layouts where the two acoustic sensingelements share a common acoustic cavity are also possible.

While in the embodiment of FIG. 14 the two acoustic sensing elements1420, 1421 both extend over the acoustic cavity 1436, in someembodiments, the acoustic coupler 1414 only acoustically couples thephysiological signal acoustic sensing element 1420 two the patient'sskin 1401, not the noise acoustic sensing element 1421. For example, theacoustic coupler 1414 can only be in physical contact with thephysiological signal acoustic sensing element 1420 without substantiallycontacting the noise acoustic sensing element 1421. In cases where theacoustic coupler 1414 is a bump such as the one described herein, thebump can only be aligned with the physiological signal acoustic sensingelement 1420, as indicated by the dashed circle 1414 in the bottom view1450 of the acoustic sensing elements 1420, 1421.

FIG. 15 is a cross-sectional schematic drawing of an embodiment of anacoustic sensor 1515 that includes a piezoelectric physiological signalacoustic sensing element 1520 and a separate noise microphone 1521. Theframe 1518, the piezoelectric film 1520, and the acoustic coupler 1514are as described and illustrated with respect to, for example, FIG. 13.However, the acoustic sensor 1515 does not include a secondpiezoelectric film to serve as the noise acoustic sensing element butinstead includes a separate microphone 1521. The noise microphone 1521can be housed, for example, in the upper cavity 1530 of the frame 1518.Other locations can also be suitable. The noise microphone 1521 can be,for example, a condenser microphone, a MEMS microphone, or anelectromagnetic induction microphone, a light-modulation microphone, ora piezoelectric microphone. The noise microphone 1521 can exhibitdirectionality such that it is more sensitive, for example, in theupward direction away from the patient's skin 1501 in order to reduceits sensitivity to the physiological sounds picked up by thephysiological signal acoustic sensing element 1520.

FIG. 16 illustrates a time plot 1602 of an acoustic physiological signalcorrupted by noise, as well as a time plot 1618 of the noise. The plot1602 of the acoustic physiological signal corrupted with noise is asimplified representation of a patient breathing. Each of the pulses1604, 1610, 1612 represents either an inhalation or exhalation. Threebursts of noise 1606, 1608, 1614 are superimposed on the physiologicalsignal. The plot 1602 represents an output from a physiological signalacoustic sensing element (e.g., 1020, 1220, 1320, 1420, 1520), asdescribed herein. The breathing sounds are acoustically coupled to thephysiological signal acoustic sensing element via an acoustic coupler,as described herein. However, the physiological signal acoustic sensingelement also picks up noise from the patient's surroundings.

The plot 1618 is a simplified representation of noise detected by annoise acoustic sensing element (e.g., 1021, 1221, 1321, 1421, 1521), asdescribed herein. In particular, there are three bursts 1620, 1622, 1624of noise. In some embodiments, it is advantageous that the bursts ofnoise 1620, 1622, 1624 in the plot 1618 share certain characteristics,and/or that they be meaningfully correlated with, the bursts of noise1606, 1608, 1614 in the physiological signal. Generally, this will bedependent upon the positioning and design of both the physiologicalsignal acoustic sensing element and the noise acoustic sensing element.For example, the amplitude of the corresponding noise bursts in therespective plots 1602, 1618 can be related by a scalar factor, a timeshift, a phase shift, or in some other way depending upon, for example,the relative placement of the two acoustic sensing elements. The outputof the noise acoustic sensing element can also contain a signalcomponent representative of the physiological sounds from the patient,though, in some embodiments, this signal component is weaker in theoutput from the acoustic sensing element than it is in the physiologicalsignal acoustic sensing element, as a result of the acoustic coupler.

FIG. 17 is a block diagram an embodiment of a noise attenuator 1740 ofan acoustic physiological monitoring system. As described herein, thenoise attenuator 1740 can be communicatively coupled with first andsecond acoustic sensing elements 1720, 1721. In some embodiments, theoutput of the first acoustic sensing element 1720 is a physiologicalsignal with noise 1730, as illustrated in plot 1602 in FIG. 16. In someembodiments, the output of the second acoustic sensing element 1721 is anoise reference signal 1731, as illustrated in plot 1618 in FIG. 16.Each of these signals 1730, 1731 is input to the noise attenuator 1740.The noise attenuator 1740 then reduces or removes the noise componentfrom the physiological signal 1730 based on information regarding thenoise component that is gleaned from the noise reference signal 1731.

The noise attenuator 1740 can use any of numerous methods and componentsfor reducing, removing, filtering, canceling, subtracting, or separatingout noise in a signal based on a noise reference signal, or combinationsof the same or the like. For example, the noise attenuator 1740 may bean adaptive noise filter or an adaptive noise canceler. The noiseattenuator 1740 can perform time domain and/or frequency domainoperations. In some embodiments, the noise attenuator 1740 employsspectral subtraction methods such as power-based, magnitude-based, ornon-linear spectral subtraction techniques. The noise attenuator 1740can include time shift modules, phase shift modules, scalar and/orcomplex multiplier modules, filter modules, etc., each of which can beimplemented using, for example, hardware (e.g., electrical components,FPGAs, ASICs, general-purpose digital signal processors, etc.) or acombination of hardware and software.

In some embodiments, the noise attenuator 1740 includes a self-adjustingcomponent whose effect on the physiological signal corrupted by noise1730 continuously varies in response to information derived from thenoise reference signal 1731. For example, the self-adjusting componentcan be an adaptive filter 1742 whose transfer function, or some othercharacteristic, is iteratively updated based on analysis of the noisereference signal 1731. The adaptive filter 1742 can be implemented, forexample, using a digital signal processor with iteratively updatedfilter coefficients. Other methods of implementing the adaptive filter1742 can also be used. Filter coefficients can be updated using, forexample, a least mean squares algorithm (LMS), or a least squaresalgorithm, a recursive least squares algorithm (RLS). The noiseattenuator 1740 can also use, for example, a Kalman filter, a jointprocess estimator, an adaptive joint process estimator, a least-squareslattice joint process estimator, a least-squares lattice predictor, anoise canceller, a correlation canceller, optimized time or frequencydomain implementations of any of the above, combinations of the same,and the like.

FIG. 18 is a block diagram of an embodiment of a signal qualitycalculator 1850 in an acoustic physiological monitoring system. Thesignal quality calculator 1850 is communicatively coupled with first andsecond acoustic sensing elements 1820, 1821. In some embodiments, oneinput to the signal quality calculator 1850 is a physiological signalcorrupted by noise 1830 (e.g., as illustrated in plot 1602 in FIG. 16),while the other input is an noise reference signal 1831 (e.g., asillustrated in plot 1618 in FIG. 16). Based, at least in part, on theseinput signals, the signal quality calculator 1850 outputs an objectivesignal quality indicator 1851.

As described herein, the signal quality calculator 1850 is a device thatis used to determine, for example, an objective indicator of the qualityof the physiological information obtained from one or more acousticsensing elements. This can be done, for example, by comparing thephysiological signal 1830 with the noise signal 1831. The signal qualitycalculator 1850 can also output an objective indicator of the degree ofconfidence in the accuracy of a physiological characteristic (e.g.,respiratory rate) determined based on the physiological informationcollected from one or more acoustic sensors.

In some embodiments, the signal quality calculator 1850 includes one ormore signal envelope detectors 1852, one or more peak detectors 1854,and a comparator 1856. The envelope detectors 1852 are used, forexample, to detect the respective amplitude envelopes 1616, 1626 of thephysiological signal 1830 and the noise reference signal 1831, asillustrated in FIG. 16. The envelope detectors 1852 can be implementedin any way known in the art. For example, the envelope detectors 1852can use squaring and low-pass filtering techniques and/or Hilberttransform techniques for envelope detection. Other techniques or devicescan also be used for envelope detection, including analog devices.

Once the amplitude envelopes of the physiological signal 1830 and thenoise reference signal 1831 have been identified, peak detectors 1854can be used to identify different peaks in the amplitude envelopes, thetemporal spacing between peaks, the relative maximum amplitude of thepeaks, the time width of the peaks, etc. For example, with reference toplot 1618, the peak detector 1854 can identify three separate peaks, onefor each illustrated bursts of acoustic noise. With reference to plot1602, the peak detector 1854 can identify five separate peaks: onecorresponding to the first pulse 1604 of breathing sounds, onecorresponding to the first burst of acoustic noise 1606, a largeramplitude peak corresponding to the second pulse of breathing soundswith superimposed noise 1610, 1608, one corresponding to the third pulseof breathing sounds 1612, and one corresponding to the third burst ofacoustic noise 1614.

Once the peaks of the amplitude envelopes have been detected, possiblyalong with information regarding the temporal spacing between the peaks,the relative heights of the peaks, their widths etc., this informationcan then be transmitted to the comparator 1856. In some embodiments, thecomparator 1856 is endowed with logic for determining an objectivesignal quality indicator based, at least in part, on the informationfrom the peak detectors 1854.

In some embodiments, the comparator 1856 can determine whether each ofthe identified peaks in the amplitude envelope of the physiologicalsignal 1830 has a corresponding peak in the amplitude envelope of thenoise signal 1831. For example, with respect to the plots 1602, 1618 inFIG. 16, the comparator 1856 can determine that the first peak in thephysiological signal 1830 (the first pulse of breathing sounds 1604)does not have a corresponding peak in the noise signal 1831 at the sametime. On this basis, the comparator 1856 could judge that the first peak1604 can well likely represent physiological information. Upon analyzingthe second peak in the physiological signal 1830 (the first burst ofnoise 1606), the comparator 1856 could note the presence of acorresponding peak 1620 in the noise reference signal 1831 at the sametime and having approximately the same height and width. On this basis,the comparator 1856 could judge that the second peak in thephysiological signal 1830 can well likely represent acoustic noise.

An analysis of the third peak in the physiological signal 1830 (thesecond pulse of breathing sounds 1610) can identify a corresponding peak1622 in the noise reference signal 1831 at the same time but having asmaller width and height than the peak 1610 in the physiological signal.On this basis, the comparator 1856 can determine that it is somewhatlikely that the third peak 1610 in the physiological signal 1830 isrepresentative of physiological information. In this way, the signalquality calculator 1850 can identify, for example, individual featuresof the time domain physiological signal 1830 and noise reference signal1831, and then determine the likelihood that each feature representsphysiological information or noise information.

The signal quality calculator 1850 can then calculate and output anindicator (e.g., a probability value, a percentage, an occurrenceindicator, a Boolean or binary value, an alarm or alert, or some otherindicator) to express the extent to which the physiological signal 1830is viewed as being indicative of actual physiological information ratherthan noise. The signal quality calculator 1850 can also output anindicator to express the confidence in a physiological characteristiccalculated from the physiological signal 1830. For example, if thesignal quality calculator 1850 determines that the physiological signal1830 is primarily composed of physiological information, then it candetermine a high confidence level in a physiological characteristic(e.g., respiratory rate) determined from the physiological signal 1830.In some embodiments, the physiological signal with reduced noise (e.g.,1741) from the noise attenuator can also serve as an input to the signalquality calculator 1850.

While a time domain method for determining signal quality is illustratedin FIG. 18, signal quality calculations could also be performed in thefrequency domain. Also, different signal quality calculation algorithmscan be used depending upon the particular type of physiologicalinformation being sensed, and the characteristics of the signals thatare representative of that physiological information.

Electromagnetic Interference (EMI) Compensation

In some embodiments, the physiological monitoring systems and patientsensors described herein include electromagnetic interferencecompensation features. The electromagnetic interference compensationfeatures can be useful for reducing any deleterious effect of EMI on theaccuracy of physiological characteristics determined using themonitoring systems. One possible source of such EMI could be, forexample, 50-60 Hz RF waves generated by the electric power distributionsystem in a patient care facility.

In some embodiments, the physiological monitoring systems include anelectrical conductor for detecting an EMI reference signal that isindicative of EMI that may have corrupted electrical signals used by thephysiological monitoring systems (e.g., a physiological signal generatedby an acoustic sensing element). The EMI reference signal detector canbe, for example, a dedicated antenna that is positioned at a locationwhere the EMI that it detects is in some way representative of, ormeaningfully correlated with, the EMI to which an electrical signalwithin the patient sensor is exposed. The EMI reference signal detectorcan be located, for example, on or in one or more wearable patientsensors (e.g., 215, 815, 915, etc.), though it may also be located in aseparate physiological monitor unit, intermediate location (e.g., cable,connector or hub), at any location described above with respect toacoustic noise reference sensing elements, or at some other location.

In some embodiments, the EMI reference signal detector is a conductiveplate or wire, or some other conductive structure. In some embodiments,the EMI reference signal detector is left electrically floating. Whilein some embodiments, the EMI reference signal detector is a dedicatedcomponent, in other embodiments other existing components of, forexample, a patient sensor described herein can be used as the EMIreference signal detector. For example, one or more electrical shieldinglayers (e.g., 226, 228) in a patient sensor can be used to detect EMIand to generate an EMI reference signal. Generally, according to certainaspects, any of the shielding barriers described herein (e.g., withrespect to FIGS. 2B-E, 5A-B, 21-22, etc.) can be used to detect EMI andgenerate an EMI reference signal.

In some embodiments, the EMI reference signal generated by the EMIreference signal detector is transmitted to a noise attenuator or othersensing circuitry. The noise attenuator can also be communicativelycoupled to, for example, one or more physiological electrical signalsoutput from the acoustic sensing elements described herein. Suchphysiological electrical signals can be corrupted by any EMI to whichthey are exposed.

The noise attenuator or other sensing circuitry reduces or removes theEMI component from the physiological signal based on informationregarding the EMI that is gleaned from the EMI reference signal. Thenoise attenuator or other sensing circuitry can use any of numerousmethods and components for reducing, removing, filtering, canceling,subtracting, or separating out EMI in a signal based on the EMIreference signal, or combinations of the same or the like. For example,the noise attenuator may be an adaptive noise filter or an adaptivenoise canceller. The noise attenuator can perform time domain and/orfrequency domain operations. The noise attenuator can include time shiftmodules, phase shift modules, scalar and/or complex multiplier modules,filter modules, etc., each of which can be implemented using, forexample, hardware (e.g., electrical components, FPGAs, ASICs,general-purpose digital signal processors, etc.) or a combination ofhardware and software.

In some embodiments, the noise attenuator or other sensing circuitryincludes a self-adjusting component whose effect on the physiologicalsignal corrupted by EMI continuously varies in response to informationderived from the EMI reference signal. For example, the self-adjustingcomponent can be an adaptive filter whose transfer function, or someother characteristic, is iteratively updated based on analysis of theEMI reference signal. The adaptive filter can be implemented, forexample, using a digital signal processor with iteratively updatedfilter coefficients. Other methods of implementing the adaptive filtercan also be used. Filter coefficients can be updated using, for example,a least mean squares algorithm (LMS), or a least squares algorithm, arecursive least squares algorithm (RLS). The noise attenuator can alsouse, for example, a Kalman filter, a joint process estimator, anadaptive joint process estimator, a least-squares lattice joint processestimator, a least-squares lattice predictor, a noise canceller, acorrelation canceller, optimized time or frequency domainimplementations of any of the above, combinations of the same, and thelike.

Additional Sensor Embodiments

FIG. 19A is a top perspective of a sensor system 1900 including a sensorassembly 1901 suitable for use with any of the physiological monitorsshown in FIGS. 1A-C and a monitor cable 1911. The sensor assembly 1901includes a sensor 1915, a cable assembly 1917 and a connector 1905. Thesensor 1915, in one embodiment, includes a sensor subassembly 1902 andan attachment subassembly 1904. The cable assembly 1917 of oneembodiment includes a cable 1907 and a patient anchor 1903. The variouscomponents are connected to one another via the sensor cable 1907. Thesensor connector subassembly 1905 can be removably attached to monitorconnector 1909 which is connected to physiological monitor (not shown)through the monitor cable 1911. In one embodiment, the sensor assembly1901 communicates with the physiological monitor wirelessly. In variousembodiments, not all of the components illustrated in FIG. 19A areincluded in the sensor system 1900. For example, in various embodiments,one or more of the patient anchor 1903 and the attachment subassembly1904 are not included. In one embodiment, for example, a bandage or tapeis used instead of the attachment subassembly 1904 to attach the sensorsubassembly 1902 to the measurement site. Moreover, such bandages ortapes may be a variety of different shapes including generally elongate,circular and oval, for example.

The sensor connector subassembly 1905 and monitor connector 1909 may beadvantageously configured to allow the sensor connector 1905 to bestraightforwardly and efficiently joined with and detached from themonitor connector 1909. Embodiments of sensor and monitor connectorshaving similar connection mechanisms are described in U.S. patentapplication Ser. No. 12/248,856 (hereinafter referred to as “the '856application”), filed on Oct. 9, 2008, which is incorporated in itsentirety by reference herein. For example, the sensor connector 1905includes a mating feature 1913 which mates with a corresponding feature(not shown) on the monitor connector 1909. The mating feature 1905 mayinclude a protrusion which engages in a snap fit with a recess on themonitor connector 1909. In certain embodiments, the sensor connector1905 can be detached via one hand operation, for example. Examples ofconnection mechanisms may be found specifically in paragraphs [0042],[0050], [0051], [0061]-[0068] and [0079], and with respect to FIGS.8A-F, 13A-E, 19A-F, 23A-D and 24A-C of the '856 application, forexample. The sensor system 1900 measures one or more physiologicalparameters of the patient, such as one of the physiological parametersdescribed above.

The sensor connector subassembly 1905 and monitor connector 1909 mayadvantageously reduce the amount of unshielded area in and generallyprovide enhanced shielding of the electrical connection between thesensor and monitor in certain embodiments. Examples of such shieldingmechanisms are disclosed in the '856 application in paragraphs[0043]-[0053], [0060] and with respect to FIGS. 9A-C, 11A-E, 13A-E,14A-B, 15A-C, and 16A-E, for example.

As will be described in greater detail herein, in an embodiment, theacoustic sensor assembly 1901 includes a sensing element, such as, forexample, a piezoelectric device or other acoustic sensing device. Thesensing element generates a voltage that is responsive to vibrationsgenerated by the patient, and the sensor includes circuitry to transmitthe voltage generated by the sensing element to a processor forprocessing. In an embodiment, the acoustic sensor assembly 1901 includescircuitry for detecting and transmitting information related tobiological sounds to a physiological monitor. These biological soundsmay include heart, breathing, and/or digestive system sounds, inaddition to many other physiological phenomena. The acoustic sensor 1915in certain embodiments is a biological sound sensor, such as the sensorsdescribed herein. In some embodiments, the biological sound sensor isone of the sensors such as those described in the '883 application. Inother embodiments, the acoustic sensor 1915 is a biological sound sensorsuch as those described in U.S. Pat. No. 6,661,161, which isincorporated by reference herein. Other embodiments include othersuitable acoustic sensors.

The attachment sub-assembly 1904 includes first and second elongateportions 1906, 1908. The first and second elongate portions 1906, 1908can include patient adhesive (e.g., in some embodiments, tape, glue, asuction device, etc.) attached to a elongate member 1910. The adhesiveon the elongate portions 1906, 1908 can be used to secure the sensorsubassembly 1902 to a patient's skin. As will be discussed in greaterdetail herein, the elongate member 1910 can beneficially bias the sensorsubassembly 1902 in tension against the patient's skin and reduce stresson the connection between the patient adhesive and the skin. A removablebacking can be provided with the patient adhesive to protect theadhesive surface prior to affixing to a patient's skin.

The sensor cable 1907 is electrically coupled to the sensor subassembly1902 via a printed circuit board (“PCB”) (not shown) in the sensorsubassembly 1902. Through this contact, electrical signals arecommunicated from the multi-parameter sensor subassembly to thephysiological monitor through the sensor cable 1907 and the cable 1911.

FIGS. 19B-19C are top and bottom perspective views of a sensor includingsubassembly 1902 and an attachment subassembly 1904 in accordance withan embodiment of the present disclosure. The attachment subassembly 1904generally includes lateral extensions symmetrically placed about thesensor subassembly 1902. For example, the attachment subassembly 1904can include single, dual or multiple wing-like extensions or arms thatextend from the sensor subassembly 1902. In other embodiments, theattachment subassembly 1902 has a circular or rounded shape, whichadvantageously allows uniform adhesion of the attachment subassembly1904 to an acoustic measurement site. The attachment subassembly 1904can include plastic, metal or any resilient material, including a springor other material biased to retain its shape when bent. In theillustrated embodiment, the attachment subassembly 1904 includes a firstelongate portion 1906, a second elongate portion 1908, an elongatemember 1910 and a button 1912. As will be discussed, in certainembodiments the attachment subassembly 1904 or portions thereof aredisposable and/or removably attachable from the sensor subassembly 1902.The button 1910 mechanically couples the attachment subassembly 1904 tothe sensor subassembly 1902. The attachment subassembly 1904 isdescribed in greater detail below with respect to FIGS. 9A-9D. Theattachment subassembly 1904 may also be referred to as an attachmentelement herein.

In one embodiment, the sensor subassembly 1902 is configured to beattached to a patient and includes a sensing element configured todetect bodily sounds from a patient measurement site. The sensingelement may include a piezoelectric membrane, for example, and issupported by a support structure such as a generally rectangular supportframe 1918. The piezoelectric membrane is configured to move on theframe in response to acoustic vibrations, thereby generating electricalsignals indicative of the bodily sounds of the patient. An electricalshielding barrier (not shown) may be included which conforms to thecontours and movements of the piezoelectric element during use. In theillustrated embodiment, additional layers are provided to help adherethe piezoelectric membrane to the electrical shielding barrier 1927.Embodiments of the electrical shielding barrier are described below withrespect to FIGS. 3A-B and FIGS. 5A-B, FIGS. 21-22, for example.

Embodiments of the sensor subassembly 1902 also include an acousticcoupler 1914, which advantageously improves the coupling between thesource of the signal to be measured by the sensor (e.g., the patient'sskin) and the sensing element. The acoustic coupler 1914 of oneembodiment includes a bump positioned to apply pressure to the sensingelement so as to bias the sensing element in tension. The acousticcoupler 1914 can also provide electrical isolation between the patientand the electrical components of the sensor, beneficially preventingpotentially harmful electrical pathways or ground loops from forming andaffecting the patient or the sensor.

The sensor subassembly 1902 of the illustrated embodiment includes anacoustic coupler 1914 which generally envelops or at least partiallycovers some or all of the components of the sensor subassembly 1902.Referring to FIG. 19C, the bottom of the acoustic coupler 1914 includesa contact portion 1916 which is brought into contact with the skin ofthe patient. Embodiments of acoustic couplers are described below withrespect to FIGS. 19D-19E, 4, and 5A-B, for example.

FIGS. 19D-19E are top and bottom exploded, perspective views,respectively, of the sensor subassembly 1902 of FIGS. 19A-C.

Support Frame

The frame generally supports the various components of the sensor. Forexample, the piezoelectric element, electrical shielding barrier,attachment element and other components may be attached to the frame.The frame can be configured to hold the various components in place withrespect to the frame and with respect to one another, therebybeneficially providing continuous operation of the sensor under avariety of conditions, such as during movement of the sensor. Forexample, the frame can be configured to hold one or more of thecomponents together with a predetermined force. Moreover, the frame caninclude one or more features which can improve the operation of thesensor. For example, the frame can include one or more cavities whichallow for the piezoelectric element to move freely and/or which amplifyacoustic vibrations from bodily sounds of the patient.

In the illustrated embodiment, a PCB 1922 is mounted on the frame 1918.The frame 1918 supports a series of layers which are generally wrappedaround the underside 1942 of the frame 1918 and include, from innermostto outermost, an inner shield layer 1926, an bonding layer 1924, asensing element 1920 and an outer shield layer 1928.

As shown in FIG. 19D, the support frame 1918 has a generally rectangularshape, as viewed from the top or bottom, although the frame shape couldbe any shape, including square, oval, elliptical, elongated, etc. Invarious embodiments, the frame 1918 has a length of from between about 5and 50 millimeters. In one embodiment, the frame 1918 has a length ofabout 17 millimeters. The relatively small size of the frame 1918 canallow the sensor subassembly 1902 to be attached comfortably tocontoured, generally curved portions of the patient's body. For,example, the sensor subassembly 1902 can be comfortably attached toportions of the patient's neck whereas a larger frame 1918 may beawkwardly situated on the patient's neck or other contoured portion ofthe patient. The size of the frame 1918 may allow for the sensorsubassembly 1902 to be attached to the patient in a manner allowing forimproved sensor operation. For example, the relatively small frame 1918,corresponding to a relatively smaller patient contact area, allows forthe sensor subassembly 1902 to be applied with substantially uniformpressure across the patient contact area.

The frame 1918 is configured to hold the various components in placewith respect to the frame. For example, in one embodiment, the frame1918 includes at least one locking post 1932, which is used to lock thePCB 1922 into the sensor sub-assembly 1902, as described below. In theillustrated embodiment, the frame 1918 includes four locking posts 1932,for example, near each of the 1918 four corners of the frame 1918. Inother embodiments, the frame 1918 includes one, two, or three lockingposts 1918. When the locking posts 1932 are brought into contact withhorns of an ultrasonic welder or a heat source, they liquefy and flow toexpand over the material beneath it and then harden in the expandedstate when the welder is removed. When the components of the sensorsub-assembly 1902 are in place, the locking posts 1932 are flowed tolock all components into a fixed position.

In one embodiment, the locking posts 1932 are formed from the samematerial as, and are integral with the frame 1918. In other embodiments,the locking posts 1932 are not formed from the same material as theframe 1918. For example, in other embodiments, the locking posts 1932include clips, welds, adhesives, and/or other locks to hold thecomponents of the sensor sub-assembly 1902 in place when the lockingposts 1932 are locked into place.

With further reference to FIG. 19E, in an assembled configuration, thePCB 1922 sits inside of an upper cavity 1930 of the frame 1918 and ispressed against the sensing element 1920 to create a stable electricalcontact between the PCB 1922 and electrical contact portions of thesensing element 1920. For example, in certain embodiments, the expandedlocking posts 1932 press downward on the PCB 1922 against the sensingelement 1920, which is positioned between the PCB 1922 and the frame1918. In this manner, a stable and sufficient contact force between thePCB 1922 and the sensing element 1920 is maintained. For example, as thesensor assembly 1900 moves due to acoustic vibrations coming from thepatient or due to other movements of the patient, the electrical contactbetween the PCB 1922 and the sensing element 1920 remains stable,constant, uninterrupted, and/or unchanged.

In another embodiment, the sensing element 1920 may be positioned overthe PCB 1922 between the expanded locking posts 1932 and the PCB 1922.In certain embodiments, the contact force between the PCB 1922 and thesensing element 1920 is from between about 0.5 pounds and about 10pounds. In other embodiments, the contact force is between about 1 poundand about 3 pounds. In one embodiment, the contact force between the PCB1922 and the sensing element 1920 is at least about 2 pounds. Thebonding layer 1924 is positioned between the frame 1918 and the sensingelement 1920 and allows, among other things, for the sensing element1920 to be held in place with respect to the frame 1918 prior toplacement of the PCB 1922. The PCB 1922 and frame 1918 includecorresponding cutout portions 1946, 1948 which are configured to acceptthe sensor cable (not shown).

The PCB cutout portion 1946 also includes a circular portion which isconfigured to accept a button post 1944 positioned in the center of thecavity 1930. The button post 1944 is configured to receive the button1912 (FIG. 19B). The frame 1918, shielding layers 1926, 1928, adhesivelayer 1924, and sensing element 1920 each include injection holes 1935extending through opposing sides of the respective components.Additionally, in an assembled configuration the injection holes 1935 ofthe various components line up with the holes 1935 of the othercomponents such that a syringe or other device can be inserted throughthe holes. Glue is injected into the holes 1935 using the syringe,bonding the assembled components together.

Referring now to FIG. 19E, a lower cavity 1936 is disposed on theunderside of the frame 1918 and has a depth d. In an assembledconfiguration, the sensing element 1920 is wrapped around the frame 1918in the direction of the transverse axis 1938 such that the lower planarportion 1962 of the sensing element 1920 stretches across the top of thelower cavity 1936. As such, the lower cavity 1936 can serve as anacoustic chamber of the multi-parameter sensor assembly. The sensingelement 1920 thus has freedom to move up into the acoustic chamber inresponse to acoustic vibrations, allowing for the mechanical deformationof the piezoelectric sensing material and generation of thecorresponding electrical signal. In addition, the chamber of certainembodiments allows sound waves incident on the sensing element toreverberate in the chamber. As such, the sound waves from the patientmay be amplified or more effectively directed to the sensing element1920, thereby improving the sensitivity of the sensing element 1920. Assuch, the cavity 1936 allows for improved operation of the sensor.

The frame may include one or more contacts extending from the framewhich press into corresponding contact strips of the PCB, helping toensure a stable, relatively constant contact resistance between the PCBand the sensing element. FIG. 19F shows a top perspective view of anembodiment of a support frame 1918 including such contacts. The frame1918 may be generally similar in structure and include one or more ofthe features of the frame shown in FIGS. 19D-19E, such as the lockingposts 332 and the upper surface 384. The frame 1918 further includes oneor more contact bumps 1920 which press into corresponding contact strips1923 (FIG. 2E) of the PCB 1922 when the sensor sub-assembly isassembled. For example, the contact bumps 1920 may include generallynarrow rectangular raised segments and may be positioned on the uppersurface 1984 of the frame 1918.

The contact bumps 1920 help ensure a stable, constant contact resistancebetween the PCB 1922 and the sensing element 1920. The contact bumps1920 are dimensioned to press a portion of the sensing element 1920 intothe PCB 1922 when the sensor subassembly 1902 is assembled. In someembodiments, the height of the contact bumps 1920 is from about 0.1 toabout 1 mm. In some embodiments, the height of the contact bumps 1920 isin the range from about 0.2 to about 0.3 mm. In one embodiment, thecontact bumps 1920 have a height of about 0.26 mm. The height isgenerally selected to provide adequate force and pressure between thesensing element 1920 and PCB 1922.

In other embodiments, the contact bumps may have different shapes. Forexample, the bumps 1920 may be generally circular, oval, square orotherwise shaped such that the bumps 1920 are configured to press intocorresponding contact strips 1923 on the PCB 1922. The contact strips1923 may be shaped differently as well. For example, the strips 1923 maybe shaped so as to generally correspond to the cross-sectional shape ofthe bumps 1920. While there are two bumps 1920 per contact strip 1923 inthe illustrated embodiment, other ratios of contact bumps 1920 tocontract strips 1923 are possible. For example, there may be one contactbump 1920 per contact strip 1923, or more than two contact bumps 1920per contact strip 1923.

Referring again to FIGS. 19D-19E, the frame 1918 includes rounded edges1934 around which the various components including the inner shield1926, the bonding layer 1924, the sending element 1920, and the outershield 1928 wrap in the direction of the transverse axis 1938. Therounded edges 1934 help assure that the sensing element 1920 and otherlayers 1926, 1924, 1928 extend smoothly across the frame 3116, and donot include wrinkles, folds, crimps and/or unevenness. Rounded edges1934 advantageously allow uniform application of the sensing element1920 to the frame 1918, which helps assure uniform, accurate performanceof the sensor assembly 1902. In addition, the dimensions of the roundedcorners and the upper cavity 1930 can help to control the tensionprovided to the sensing element 1920 when it is stretched across theframe 1918.

The frame 1918 may have different shapes or configurations. For example,in some embodiments, the frame 1918 does not include a recess 1930 andthe PCB 1922 sits on top of the frame 1918. In one embodiment the edges1934 are not rounded. The frame 1918 may be shaped as a board, forexample. The frame 1918 may include one or more holes. For example, theframe 1918 includes four elongate bars connected to form a hollowrectangle in one configuration. In various embodiments, the frame 1918may not be generally rectangular but may instead be generally shaped asa square, circle, oval or triangle, for example. The shape of the frame1918 may be selected so as to advantageously allow the sensorsubassembly 1902 to be applied effectively to different areas of thebody, for example. The shape of the frame 1918 may also be selected soas to conform to the shape of one or more of the other components of thesensor system 1900 such as the sensing element 1920.

In addition, in some embodiments, one or more of the inner shield 1926,the bonding layer 1924, the sensing layer 1920 and the outer shield 1928are not wrapped around the frame 1918. For example, in one embodiment,one or more of these components are generally coextensive with andattached to the underside of the frame 1918 and do not include portionswhich wrap around the edges 1934 of the frame.

Sensing Element

The sensing element 1920 of certain embodiments is configured to senseacoustic vibrations from a measurement site of a medical patient. In oneembodiment, the sensing element 1920 is a piezoelectric film, such asdescribed in U.S. Pat. No. 6,661,161, incorporated in its entirety byreference herein, and in the '883 application. Referring still to FIGS.19D-19E, the sensing element 1920 includes upper portions 1972 and lowerplanar portion 1962. As will be discussed, in an assembledconfiguration, the top of the upper portions 1972 include electricalcontacts which contact electrical contacts on the PCB 1922, therebyenabling transmission of electrical signals from the sensing element1920 for processing by the sensor system. The sensing element 1920 canbe formed in a generally “C” shaped configuration such that it can wraparound and conform to the frame 1918. Sensing elements in accordancewith embodiments described herein can also be found in the '883application. In some embodiments, the sensing element 1920 includes oneor more of crystals of tourmaline, quartz, topaz, cane sugar, and/orRochelle salt (sodium potassium tartrate tetrahydrate). In otherembodiments, the sensing element 1920 includes quartz analogue crystals,such as berlinite (AlPO₄) or gallium orthophosphate (GaPO₄), or ceramicswith perovskite or tungsten-bronze structures (BaTiO₃, SrTiO₃,Pb(ZrTi)O₃, KNbO₃, LiNbO₃, LiTaO₃, BiFeO₃, Na_(x)WO₃, Ba₂NaNb₅O₅,Pb₂KNb₅O₁₅).

In other embodiments, the sensing element 1920 is made from apolyvinylidene fluoride plastic film, which develops piezoelectricproperties by stretching the plastic while placed under a high poolingvoltage. Stretching causes the film to polarize and the molecularstructure of the plastic to align. For example, stretching the filmunder or within an electric field causes polarization of the material'smolecules into alignment with the field. A thin layer of conductivemetal, such as nickel-copper or silver is deposited on each side of thefilm as electrode coatings, forming electrical poles. The electrodecoating provides an electrical interface between the film and a circuit.

In operation, the piezoelectric material becomes temporarily polarizedwhen subjected to a mechanical stress, such as a vibration from anacoustic source. The direction and magnitude of the polarization dependupon the direction and magnitude of the mechanical stress with respectto the piezoelectric material. The piezoelectric material will produce avoltage and current, or will modify the magnitude of a current flowingthrough it, in response to a change in the mechanical stress applied toit. In one embodiment, the electrical charge generated by thepiezoelectric material is proportional to the change in mechanicalstress of the piezoelectric material.

Piezoelectric material generally includes first and second electrodecoatings applied to the two opposite faces of the material, creatingfirst and second electrical poles. The voltage and/or current throughthe piezoelectric material are measured across the first and secondelectrical poles. Therefore, stresses produced by acoustic waves in thepiezoelectric material will produce a corresponding electric signal.Detection of this electric signal is generally performed by electricallycoupling the first and second electrical poles to a detector circuit. Inone embodiment, a detector circuit is provided with the PCB 1922, asdescribed in greater detail below.

By selecting the piezoelectric material's properties and geometries, asensor having a particular frequency response and sensitivity can beprovided. For example, the piezoelectric material's substrate andcoatings, which generally act as a dielectric between two poles, can beselected to have a particular stiffness, geometry, thickness, width,length, dielectric strength, and/or conductance. For example, in somecases stiffer materials, such as gold, are used as the electrode. Inother cases, less stiff materials, such as silver, are employed.Materials having different stiffness can be selectively used to providecontrol over sensor sensitivity and/or frequency response.

The piezoelectric material, or film, can be attached to, or wrappedaround, a support structure, such as the frame 1918. As shown in FIGS.19D-19E, the geometry of the piezoelectric material can be selected tomatch the geometry of the frame. Overall, the sensor can optimized topick up, or respond to, a particular desired sound frequency, and notother frequencies. The frequency of interest generally corresponds to aphysiological condition or event that the sensor is intended to detect,such as internal bodily sounds, including, cardiac sounds (e.g., heartbeats, valves opening and closing, fluid flow, fluid turbulence, etc.),respiratory sounds (e.g., breathing, inhalation, exhalation, wheezing,snoring, apnea events, coughing, choking, water in the lungs, etc.), orother bodily sounds (e.g., swallowing, digestive sounds, gas, musclecontraction, joint movement, bone and/or cartilage movement, muscletwitches, gastro-intestinal sounds, condition of bone and/or cartilage,etc.).

The surface area, geometry (e.g., shape), and thickness of thepiezoelectric material 1920 generally defines a capacitance. Thecapacitance is selected to tune the sensor to the particular, desiredfrequency of interest. Furthermore, the frame 1918 is structured toutilize a desired portion and surface area of the piezoelectricmaterial.

The capacitance of the sensor can generally be expressed by thefollowing relationship: C=ε S D, where C is the sensor's capacitance, εis the dielectric constant associated with the material type selected, Sis the surface area of the material, and D is the material thickness(e.g., the distance between the material's conducive layers). In oneembodiment, the piezoelectric material (having a predeterminedcapacitance) is coupled to an sensor impedance (or resistance) toeffectively create a high-pass filter having a predetermined high-passcutoff frequency. The high-pass cutoff frequency is generally thefrequency at which filtering occurs. For example, in one embodiment,only frequencies above the cutoff frequency (or above approximately thecutoff frequency) are transmitted.

The amount of charge stored in the conductive layers of thepiezoelectric material 1920 is generally determined by the thickness ofits conductive portions. Therefore, controlling material thickness cancontrol stored charge. One way to control material thickness is to usenanotechnology or MEMS techniques to precisely control the deposition ofthe electrode layers. Charge control also leads to control of signalintensity and sensor sensitivity. In addition, as discussed above,mechanical dampening can also be provided by controlling the materialthickness to further control signal intensity and sensor sensitivity.

In addition, controlling the tension of the sensing element 1920 in theregion where the mechanical stress (e.g., mechanical stress due toacoustic vibration from a patient's skin) is incident upon the sensingelement 1920 can serve to improve the sensitivity of the sensing element1920 and/or the coupling between the source of the signal (e.g., thepatient's skin) and the sensing element 1920. This feature will bediscussed in greater detail below with respect to the coupler 1914.

One embodiment of a piezoelectric sensing element 2000 is provided inFIGS. 20A-C. The sensing element 2000 includes a substrate 2002 andcoatings 2004, 2006 on each of its two planar faces 2008, 2010. Theplanar faces 2008, 2010 are substantially parallel to each other. Atleast one through hole 2012 extends between the two planar faces 2008,2010. In one embodiment, the sensing element 2000 includes two or threethrough holes 2012.

In one embodiment, a first coating 2004 is applied to the first planarface 2008, the substrate 2002 wall of the through holes 2012, and afirst conductive portion 2014 of the second planar face 2010, forming afirst electrical pole. By applying a first coating 2004 to the throughholes 2012, a conductive path is created between the first planar face2008 and the first conductive portion 2014 of the sensing element 2000.A second coating 2006 is applied to a second conductive portion 2016 ofthe second planar face 2010 to form a second electrical pole. The firstconductive portion 2014 and second conductive portion 2016 are separatedby a gap 2018 such that the first conductive portion 2014 and secondconductive portion 2016 are not in contact with each other. In oneembodiment, the first conductive portion 2014 and second conductiveportion 2016 are electrically isolated from one another.

In some embodiments, the first and second conductive portions 2014, 2016are sometimes referred to as masked portions, or coated portions. Theconductive portions 2014, 2016, can be either the portions exposed to,or blocked from, material deposited through a masking, or depositionprocess. However, in some embodiments, masks aren't used. Either screenprinting, or silk screening process techniques can be used to create thefirst and second conductive portions 2014, 2016.

In another embodiment, the first coating 2004 is applied to the firstplanar face 2008, an edge portion of the substrate 2002, and a firstconductive portion 2014. By applying the first coating 2004 to an edgeportion of the substrate 2002, through holes 2012 can optionally beomitted.

In one embodiment, the first coating 2004 and second coating 2006 areconductive materials. For example, the coatings 2004, 2006 can includesilver, such as from a silver deposition process. By using a conductivematerial as a coating 2004, 2006, the multi-parameter sensor assemblycan function as an electrode as well.

Electrodes are devices well known to those of skill in the art forsensing or detecting the electrical activity, such as the electricalactivity of the heart. Changes in heart tissue polarization result inchanging voltages across the heart muscle. The changing voltages createan electric field, which induces a corresponding voltage change in anelectrode positioned within the electric field. Electrodes are typicallyused with echo-cardiogram (EKG or ECG) machines, which provide agraphical image of the electrical activity of the heart based uponsignal received from electrodes affixed to a patient's skin.

Therefore, in one embodiment, the voltage difference across the firstplanar face 2008 and second planar face 2010 of the sensing element 2000can indicate both a piezoelectric response of the sensing element 2000,such as to physical aberration and strain induced onto the sensingelement 2000 from acoustic energy released from within the body, as wellas an electrical response, such as to the electrical activity of theheart. Circuitry within the sensor assembly and/or within aphysiological monitor (not shown) coupled to the sensor assemblydistinguish and separate the two information streams. One such circuitrysystem is described in U.S. Provisional No. 60/893,853, filed Mar. 8,2007, titled, “Multi-parameter Physiological Monitor,” which isexpressly incorporated by reference herein.

Referring still to FIGS. 20A-C, the sensing element 2000 is flexible andcan be wrapped at its edges, as shown in FIG. 20C. In one embodiment,the sensing element 2000 is the sensing element 1920 wrapped around theframe 1918, as shown in FIGS. 19D and 19E. In addition, by providingboth a first conductive portion 2014 and a second conductive portion2016, both the first coating 2004 and second coating 2006 and thereforethe first electrical pole of and the second electrical pole of thesensing element 2000 can be placed into direct electrical contact withthe same surface of the PCB, such as the PCB 1922 as shown FIGS. 5A-Bbelow. This advantageously provides symmetrical biasing of the sensingelement 2000 under tension while avoiding uneven stress distributionthrough the sensing element 2000.

Bonding Layer

Referring back to FIGS. 19D-19E, the bonding layer 1924 (sometimesreferred to as an insulator layer) of certain embodiments is anelastomer and has adhesive on both of its faces. In other embodiments,the bonding layer 1924 is a rubber, plastic, tape, such as a cloth tape,foam tape, or adhesive film, or other compressible material that hasadhesive on both its faces. For example, in one embodiment, the bondinglayer 1924 is a conformable polyethylene film that is double coated witha high tack, high peel acrylic adhesive. The bonding layer 1924 in someembodiments is about 2, 4, 6, 8 or 10 millimeters thick.

The bonding layer 1924 advantageously forms a physical insulation layeror seal between the components of the sensor subassembly 1902 preventingsubstances entering and/or traveling between certain portions of thesensor subassembly 1902. In many embodiments, for example, the bondinglayer 1924 forms a physical insulation layer that is water resistant orwater proof, thereby providing a water-proof or water-resistant seal.The water-resistant properties of the bonding layer 1924 provides theadvantage of preventing moisture from entering the acoustic chamber orlower cavity 1936. In certain embodiments, the sensing element 1920, thebonding layer 1924 and/or the shield layers 1926, 1928 (described below)form a water resistant or water proof seal. The seal can preventmoisture, such as perspiration, or other fluids, from entering portionsof the sensor subassembly 1902, such as the cavity 1936 when worn by apatient. This is particularly advantageous when the patient is wearingthe multi-parameter sensor assembly 1900 during physical activity. Thewater-resistant seal prevents current flow and/or a conductive path fromforming from the first surface of the sensing element 1920 to its secondsurface or vice versa as a result of patient perspiration or some othermoisture entering and/or contacting the sensing element 1920 and/orsensor assembly 1915.

The bonding layer 1924 can also provide electrical insulation betweenthe components of the sensor subassembly 1902, preventing the flow ofcurrent between certain portions of the sensor subassembly 1902. Forexample, the bonding layer 1924 also prevents the inside electrical polefrom shorting to the outside electrical pole by providing electricalinsulation or acting as an electrical insulator between the components.For example, in the illustrated embodiment, the bonding layer 1924provides electrical insulation between the sensing element 1920 and theinner shield layer 1926, preventing the inside electrical pole of thesensing element 1920 from shorting to the outside electrical pole. Inanother embodiment, a bonding layer is placed between the outer surfaceof the sensing element 1920 and the outer shield layer 1928.

The elasticity or compressibility of the bonding layer 1924 can act as aspring and provide some variability and control in the pressure andforce provided between the sensing element 1920 and PCB 1922. In someembodiments, the sensor assembly does not include a bonding layer 1924.

Electrical Noise Shielding Barrier

An electrical noise shielding barrier can electrically shield theelectrical poles of the sensing element from external electrical noises.In some embodiments the electrical shielding barrier can include one ormore layers which form a Faraday cage around a piezoelectric sensingelement, and which distribute external electrical noise substantiallyequally to the electrical poles of the piezoelectric sensing element. Inaddition, the shielding barrier flexibly conforms to the surface shapeof the piezoelectric element as the surface shape of the piezoelectricelement changes, thereby improving the shielding and sensor performance.

Referring still to FIGS. 19D-19E, the electrical shielding barrier 1927of the illustrated embodiment includes first and second shield layers1926, 1928 (also referred to herein as inner and outer shield layers1926, 1928) which form a Faraday cage (also referred to as a Faradayshield) which encloses the sensing element 1920 and acts to reduce theeffect of noise on the sensing element from sources such as externalstatic electrical fields, electromagnetic fields, and the like. As willbe described, one or more of the inner and outer shield layers 1926,1928 advantageously conform to the contours of the sensing element 1920during use, allowing for enhanced shielding of the sensing element fromexternal electrical noise.

The inner and outer shield layers 1926, 1928 include conductivematerial. For example, the inner and outer shield layers 1926, 1928include copper in certain embodiments and are advantageously formed froma thin copper tape such that the layers can conform to the shape,contours and topology of the sensor element 1920 and the frame 1918. Insome configurations, other materials (e.g., other metals) or othercombinations of materials can be used. Moreover, as described hereinwith respect to FIGS. 19-22, the electrical shielding barrier 1927 orportions thereof, such as one or more of the first and second shieldlayers 1926, 1928, can be formed from piezoelectric films. In suchembodiments, the sensor 1915 can include first and second piezoelectricfilms arranged in a stack, and the shielding barrier 1927 can be formedfrom the outer electrode of each film in the stack.

In various embodiments, one or more of the inner and outer shield layers1926, 1928 are from between about 0.5 micrometer and 10 micrometersthick. For example, the shield layers 1926, 1928, may be from betweenabout 1.5 and about 6 micrometers thick. In one embodiment, the innerand outer shield layers 1926, 1928 include copper tape about 3micrometers thick. In yet other embodiments, the shield layers 1926,1928 may be greater than 10 micrometers thick or less than 0.5micrometers thick. In general, the thickness of the shield layer 1926,1928 is selected to provide improved electrical shielding while allowingfor the shield layers 1926, 1928 to conform to the sensor element 1920and/or the frame 1918. The inner shield layer 1926 includes an adhesiveon the inside surface 1952 such that it can adhere to the frame 1918.The inner shield layer 1926 adheres directly to the frame 1918 andadvantageously conforms to the contours of the frame such as the roundededges 1934 and the lower cavity 1936, adhering to the surface 1950defining the base of the cavity 1936. The bonding layer 1924 (e.g., atape adhesive) is wrapped around and generally conforms to the contoursof the inner shield layer 1926 and the frame 1918. The sensing element1920 is wrapped around the bonding layer 1924, the inner shield layer1924 and the frame 1918. The outer shield layer 1928 is wrapped aroundand advantageously conforms to the contours of the sensing element 1920and the frame 1918. In certain embodiments, a bonding or insulatinglayer is positioned between the sensing element 1920 and the outershielding layer 1928 as well. As such, the sensing element 1920 issandwiched between and enclosed within the inner and outer shield layers1926, 1928 which form a Faraday cage around the sensing element 1920.The configuration of the shield layers 1926, 1928, the sensing element1920 and the bonding layer 1924 will be described in greater detailbelow with respect to FIGS. 5A-B.

In certain embodiments, the shield layers 1926, 1928 are coupled to acommon potential (e.g., ground) or are otherwise operatively coupled,and each of the shield layers 1926, 1928 are also electrically (e.g.,capacitively) coupled to one of the poles of the sensing element 1920.For example, the shielding layer 1926 may be capacitively coupled to thefirst electrode of the sensing element 1920, and the shielding layer1928 may be capacitively coupled to the second electrode of the sensingelement 1920.

As discussed, the electrical shielding barrier 1927 such as the Faradaycage formed by the inner and outer shield layers 1926, 1928 helps toreduce the effect of noise electrical noise on the sensing element 1920from sources such as external static electrical fields andelectromagnetic fields, thereby lowering the noise floor, providingbetter noise immunity, or both. For example, the electrical shieldingbarrier 1927 allows for the removal of electrical interference or noiseincident directed towards the sensing element 1920 while allowing thenon-noise component of the sensed signal indicative of bodily sounds tobe captured by the sensor 1915. For example, in one embodiment thesensing element 1920 is a piezoelectric film such as one of thepiezoelectric films described herein having positive and negativeelectrical poles and configured in a differential mode of operation. Theelectrical shielding barrier 1927 acts to balance the effect of thenoise by distributing at least a portion of the noise substantiallyequally to the positive and negative electrical poles of thepiezoelectric element. In some embodiments, the electrical shieldingbarrier 1927 distributes the noise equally to both the positive andnegative poles. Moreover, the noise signals distributed to the positiveand negative electrical poles are substantially in phase or actually inphase with each other. For example, the noise signals distributed to thepositive and negative poles are substantially similar frequencies and/oramplitudes with substantially no phase shift between them.

For example, in certain embodiments, noise incident on the shieldingbarrier 1927 is substantially equally distributed to each of theshielding layers 1926, 1928 because these layers are at a commonpotential (e.g., ground). The substantially equally distributed noisemay then be coupled (e.g., capacitively coupled) to the poles of thesensing element 1920. In certain embodiments, at least some of theexternal electrical noise is shunted or otherwise directed to ground bythe shield layers 1926, 1928 instead of, or in addition to, beingdistributed to the poles of the sensing element 1920.

Because the noise signal components on the positive and negative polesare substantially in phase, the difference between the noise componentson the respective poles is negligible or substantially negligible. Onthe other hand, the difference between the differential non-noise sensorsignal components indicative of bodily sounds on the positive andnegative poles will be non-zero because the sensing element isconfigured in a differential mode. As such, the noise signals canadvantageously be removed or substantially removed through a common-moderejection technique.

For example, a common-mode rejection element may receive a signalincluding the combined noise and non-noise sensor signal components ofthe positive and negative poles, respectively. The common-mode rejectionelement is configured to output a value indicative of the differencebetween the combined signal on the positive pole and the combined signalon the negative pole. Because the difference between the noise signalsis negligible, the output of the common-mode rejection element will besubstantially representative of the non-noise component of the sensorsignal and not include a significant noise component. The common moderejection element may include, for example, an operational amplifier. Inone embodiment, for example, three operational amplifiers (not shown)are used and they are disposed on the PCB 1922.

Because the shielding layers 1926, 1928 conform to the topology of theframe 1918 and the sensing element 1920, the shielding layers 1926, 1928are physically closer to the electrical poles of the sensing element1920 and are more uniformly displaced from the sensing element 1920.Moreover, the outer shield layer 1928 of certain embodiments activelymoves with and conforms to the contours of the sensing element 1920during use, such as when the sensor assembly is placed against the skinor when the sensing element 1920 is moving due to acoustic vibrations.For example, when placed against the skin, the coupling element 1958pushes against both the outer shielding layer 1928 of the shieldingbarrier 1927 and the sensing element 1920, causing them to curve alongthe inside surface of the coupling element 1958 (FIG. 5A). Because thecage is flexible and can conform to the movement of the shieldingelement 1920, the shielding performance and sensor performance isimproved. This arrangement provides advantages such as for example, forthe noise signals to be more accurately and evenly distributed to thepositive and negative electrical poles of the sensing element 1920 bythe shielding layers 1926, 1928, thereby providing enhanced noisereduction. This arrangement can also provide for improvedmanufacturability and a more stream-lined design.

Alternative configurations for the electrical shielding barrier 1927 arepossible. For example, the inner shield layer may not include anadhesive layer and may, for example, be held in place against the frame1918 by pressure (e.g., from the locking posts 1932). The outer shield1928 may also include an adhesive layer in some embodiments. In variousother embodiments, the shield layers 1926, 1928 may include othermaterials such as other types of metals. One or more of the shieldlayers may be relatively rigid in some configurations. In oneembodiment, an insulating layer or bonding layer is disposed betweensensing element 1920 and the outer shield layer 1928. In someembodiments, the inner shield layer 1926 actively conforms to thecontours of the sensing element 1920 during use in addition to the outershield layer 1928. In another embodiment, the inner shield layer 1926actively conforms to the sensing element 1920 during use and the outershield layer 1928 does not. In yet other embodiments, the sensorassembly 1901 does not include an electrical shielding barrier 1927.

Acoustic Coupler

The sensor may also include an acoustic coupler or biasing element,which advantageously improves the coupling between the source of thesignal to be measured by the sensor (e.g., the patient's skin) and thesensing element. The acoustic coupler generally includes a couplingportion positioned to apply pressure to the sensing element so as tobias the sensing element in tension. For example, the acoustic couplermay include one or more bumps, posts or raised portions which providesuch tension. The bumps, posts or raised portions may be positioned onthe inner surface of the coupler, the outer surface of the coupler, orboth and may further act to evenly distribute pressure across thesensing element. In addition, the acoustic coupler can be furtherconfigured to transmit bodily sound waves to the sensing element. Theacoustic coupler can also be configured to provide electrical isolationbetween the patient and the electrical components of the sensor.

In the illustrated embodiment, the acoustic coupler 1914 houses theother components of the sensor subassembly including the frame 1918, thePCB 1922, the shield layers 1926, 1928, the bonding layers 1924 and thesensing element 1920. The acoustic coupler 1914 includes anon-conductive material or dielectric. As shown, the acoustic coupler1914 generally forms a dielectric barrier between the patient and theelectrical components of the sensor assembly 1901. As such, the acousticcoupler 1914 provides electrical isolation between the patient and theelectrical components of the sensor subassembly 1902. This isadvantageous in avoiding potential harmful electrical pathways or groundloops forming between the patient and the sensor.

As shown in FIGS. 19D-19E, the acoustic coupler 1914 is formed in ahollow shell capable of housing the components of the other sensorsubassembly 1902. Referring to FIG. 19D, the acoustic coupler 1914 ofthe illustrated embodiment also includes recesses 1956 and holes 1952capable of receiving and securing the button 1912 (FIG. 19B) andportions of the elongate member 1910 (FIG. 19B) of the attachmentsubassembly 1904.

FIG. 21 is a cross-sectional view of the acoustic coupler 1914 takenalong the line 21-21. In certain embodiments, the acoustic couplerincludes a bump or protrusion on the inner surface of the coupler 1914and configured to advantageously bias the sensing membrane in tension.For example, a coupling element 1958 is disposed on the on the interiorbottom portion of the acoustic coupler 1914 and which biases the sensingelement 1920 in tension. The coupling element 1958 of the illustratedembodiment is a generally rectangular bump which extends by a height habove the cavity 1960 which is formed on the interior bottom of theacoustic coupler 1914. The coupling element 1958 is centered about andextends along the longitudinal axis 1940 (FIGS. 19D and 19E) from nearthe front of the acoustic coupler 1914 to near the back of the acousticcoupler 1914. In the illustrated embodiment, the coupling element 1958is about ¼ of the width of the acoustic coupler 1914 along thetransverse axis 1938. As will be discussed in greater detail below withrespect to FIG. 22A-B, the coupling element 1958 can advantageously biasthe sensing element 1920 in tension by applying pressure to the sensingelement 1920. Because the sensing element 1920 may be generally taut intension under the pressure of the coupling bump 1958, the sensingelement 1920 will be mechanically coupled to the coupling bump 1958 andresponsive to acoustic vibrations travelling through the coupler 1914 tothe sensing element 1920, thereby providing improved coupling betweenthe patient's skin and the sensing element 1920. As such, the acousticcoupler 1914 provides for improved measurement sensitivity, accuracy, orboth, among other advantages.

The acoustic coupler 1914 is further configured to transmit bodily soundwaves to the sensing element 1920. The coupler 1914 can further includea portion disposed on the outer surface of the coupler 1914 and which isconfigured to contact the skin during use. For example, the acousticcoupler 1914 can include an outer protrusion, bump or raised portion onthe outer surface. Referring to FIGS. 19E and 4, the underside of theacoustic coupler 1914 includes portion 1916 which is configured tocontact the skin of the patient and can provides contact between theskin and the acoustic coupler 1914. Acoustic vibrations from the skinwill be incident on the portion 1916, travel through the acousticcoupler to the coupling bump 1958 and eventually be incident on thesensing element 1920 held in tension by the bump 1958. In addition, thecontact portion 1916 may, in conjunction with the coupling element 1958or on its own, also help to improve the coupling between the skin andthe sensing element 1920. For example, when pressed against the skin,the contact portion 1916 may push a portion of the inner surface of thecoupler 1914, such as the coupling element 1958, into the sensingelement 1920, advantageously holding the sensing element 1920 intension. As shown, the contact portion 1916 of the illustratedembodiment includes a semi-cylindrical bump mounted generally underneaththe coupling element 1958. Similar to the coupling element 1958, thecontact portion 1916 is centered about and extends along thelongitudinal axis 1940 from near the front of the acoustic coupler 1914to near the back of the acoustic coupler 1914. Moreover, the acousticcoupler 1914 acts to evenly distribute pressure to the sensing element1920 during use. For example, because the coupling element 1958 and theportion 1916 are generally positioned such that they are centered withrespect to surface of the sensing element 1920, pressure will bedistributed symmetrically and/or evenly across the sensing element 1920.

Referring to FIG. 19E, a pair of slots 1964 are disposed on either endof the contact portion 1916 and each run generally along the transverseaxis from near the left side of the acoustic coupler 1914 to the rightside of the acoustic coupler 1914. The slots serve to decouple a segment1966 of the bottom of the acoustic coupler 1914 including the couplingelement 1958 and the contact portion 1916 from the remainder of theacoustic coupler 1914. As such, the segment 1966 can move at leastpartially independent from the rest of the acoustic coupler 1914 inresponse to acoustic vibrations on the skin of the patient, therebyefficiently transmitting acoustic vibrations to the sensing element1920. The acoustic coupler 1914 of certain embodiments includes anelastomer such as, for example, rubber or plastic material.

In an alternative embodiment of the acoustic coupler 1914, for example,the acoustic coupler 1914 does not include a hollow shell and does nothouse the other components of the sensor subassembly. For example, thecoupler 1914 may include a single planar portion such as, for example, aboard which couples to the underside of the frame 1918 such that theshielding layers 1926, 1928, the sensing element 1920 and the bondinglayer 1924 are positioned between the coupler 1914 and the frame 1918.In some configurations, the coupler 1914 is positioned between the frame1918 and one or more of the shielding layers 1926, 1928, the sensingelement 1920 and the bonding layer 1924. Moreover, the acoustic coupler1914 may include a dielectric material, which advantageouslyelectrically isolates the electrical components of the sensorsubassembly 1902 from the patient. For example, the dielectric layer mayensure that there is no electrical connection or continuity between thesensor assembly and the patient.

In certain embodiments, portions of the sensor assembly such as, forexample, the acoustic coupler 1914 may include a gel or gel-likematerial. The gel may provide beneficial acoustic transmission, forexample, serving to enhance the coupling between the acoustic vibrationsfrom the patient's skin and the sensing element 1920. The gel mayprovide acoustic impedance matching, for example, between the skin andthe sensor. For example, the gel may serve to reduce the impedancemismatch from potential skin-to-air and air-to-sensing elementdiscontinuity, thereby reducing potential reflections and signal loss.The gel may be embedded in a portion of the acoustic coupler 1914. Forexample, one or more of the coupling element 1958 and the contactportion 1916 may include a gel or gel-like material. The acousticcoupler 1914 may include an embedded gel in certain embodiments whereone or more of the coupling element 1958 and the contact portion 1916are not included. For example, the entire patient contact portion of theacoustic coupler 1914 may include gel material extending substantiallyfrom the patient contact surface to the interior of the coupler 1914across the contact portion. One or more columns of gel material mayextend from the patient contact surface of the coupler 1914 to theinterior of the coupler 1914 in other embodiments. In yet furtherembodiments, the gel is not embedded in the acoustic coupler 1914 but isadded to the skin directly. In one embodiment, the gel is embedded inthe acoustic coupler 1914 and is configured to be released from thecoupler 1914 when the sensor assembly is applied to the patient. Forexample, gel can be filled in one or more cavities of the acousticcoupler 1914 prior to use wherein the cavities are configured to openand release the gel when the coupler is pressed against the skin.

FIGS. 22A-B are cross-sectional views of the sensor subassembly 1902 ofFIG. 19 along the lines 22A-22A and 22B-22B, respectively. As shown, theinner copper shield 1926 is positioned as the inner most of the shieldlayers 1926, 1928, the bonding layer 1924 and the sensing element 1920.Referring to FIGS. 19D-E and FIGS. 22A-B, the four tabs 1968 of theinner copper shield 1926 are flat and extend across the top of the framerecess 1930 and the four corners of the top surface of the PCB (notshown in FIGS. 22A-B) which sits in the frame recess 1930. The bondinglayer 1924 is wrapped around the inner copper shield 1926. The upperportions 1970 of the bonding layer 1924 bend downward to conform to theshape of the frame 1918 such that they extend across and contact thebottom of the frame cavity 1930. The sensing element 1920 is wrappedaround the bonding layer 1924 and the upper portions 1972 of the sensingelement 1920 also bend downward to conform to the shape of the frame1918. As such, the upper portions 1972 of the sensing element 1920extend across the bottom of the frame cavity 1930 and are in contactwith the bottom of the PCB 1922 and the top surface of the bonding layer1924. The outer copper layer 1928 is wrapped around the sensing element1920 and the upper planar portions 1973 of the outer copper shield 1928are flat, extend across the top of the frame recess 1930, and are incontact with the top surface of the PCB (not shown).

The shield layers 1926, 1928, the bonding layer 1924 and the sensingelement 1920 wrap around the rounded edges 1934 of the frame 1918. Thelower planar portions 1974, 1976 of the inner shield layer 1926 and thebonding layer 1924 bend upwards so as extend across the bottom surface1950 of the frame 1918. The lower planar portions 1962, 1980 of thesensing element 1920 and the outer shield layer 1928, on the other hand,extend between the lower frame cavity 1936 and the coupler cavity 1960.Moreover, the lower planar portions 1962, 1980 of the sensing element1920 and the outer shield layer 1928 extend across the top of thecoupling portion 1958. Because the coupler portion 1958 extends slightlyabove the coupler cavity 1960 into the lower frame cavity 1936 by thedistance h, the sensing element 1920 is advantageously biased in tensionimproving the sensitivity of the sensing element 1920, the coupling ofthe sensing element 1920 to acoustic vibrations in the skin of thepatient (not shown), or both.

In various embodiments, the components of the sensor subassembly 1902may be arranged differently. For example, the components may be combinedsuch that the overall assembly include fewer discrete components,simplifying manufacturability. In one embodiment, one or more of theshielding layers 1926, 1928, the bonding layer 1924 and the sensingelement 1920 may include an integral portion (e.g., a multi-layeredfilm). In some embodiments, more than one bonding layer 1924 is used. Inone embodiment, adhesive layers are formed on one or more of theshielding layers 1926, 1928 and the sensing element 1920, and noseparate bonding layer 1924 is present. In another embodiment, thevarious layers are held together by pressure (e.g., from the contactposts 1932 and/or PCB) instead of through the use of adhesives.

Referring still to FIGS. 19D-E and 22A-B, a method for attaching theshielding layers 1926, 1928, the bonding layer 1924, the sensing element1920 and the PCB 1922 to the frame 1918 includes providing the innershield 1926 and attaching it to the frame 1918. The sensing element 1920and bonding layer 1924 are provided and also attached to the frame 1918.A printed circuit board 1922 is then provided. The printed circuit board1922 is placed on top of the sensing element 1920 such that a first edge1980 of the printed circuit board 1922 is placed over a first conductiveportion of the sensing element 1920, and a second edge 1982 of theprinted circuit board 1922 is placed over a second conductive portion ofthe sensing element 1920.

The printed circuit board 1922 is pressed down into the sensing element1920 in the direction of the frame 1918. As the printed circuit board1922 is pressed downward, the contact bumps (not shown) of the frame1918 push the bonding layer 1924 and sensing element 1920 into contactstrips located along the first and second sides or edges 1980, 1982 ofthe printed circuit board 1922. The contact strips of the printedcircuit board 1922 are made from conductive material, such as gold.Other materials having a good electro negativity matching characteristicto the conductive portions of the sensing element 1920, may be usedinstead. The elasticity or compressibility of the bonding layer 1924acts as a spring, and provides some variability and control in thepressure and force provided between the sensing element 1920 and printedcircuit board 1922.

Once the outer shield 1928 is provided and attached to the frame 1918, adesired amount of force is applied between the PCB 1922 and the frame1918 and the locking posts 1932 are vibrated or ultrasonically or heateduntil the material of the locking posts 1932 flows over the PCB 1922.The locking posts 1932 can be welded using any of a variety oftechniques, including heat staking, or placing ultrasonic welding hornsin contact with a surface of the locking posts 1932, and applyingultrasonic energy. Once welded, the material of the locking posts 1932flows to a mushroom-like shape, hardens, and provides a mechanicalrestraint against movement of the PCB 1922 away from the frame 1918 andsensing element 1920. By mechanically securing the PCB 1922 with respectto the sensing element 1920, the various components of the sensorsub-assembly 1902 are locked in place and do not move with respect toeach other when the multi-parameter sensor assembly is placed intoclinical use. This prevents the undesirable effect of inducingelectrical noise from moving assembly components or inducing instableelectrical contact resistance between the PCB 1922 and the sensingelement 1920. In certain embodiments, the locking posts 1932 providethese advantages substantially uniformly across multiple sensors.

Therefore, the PCB 1922 can be electrically coupled to the sensingelement 1920 without using additional mechanical devices, such as rivetsor crimps, conductive adhesives, such as conductive tapes or glues, likecyanoacrylate, or others. In addition, the mechanical weld of thelocking posts 1932 helps assure a stable contact resistance between thePCB 1922 and the sensing element 1920 by holding the PCB 1922 againstthe sensing element 1920 with a constant pressure, for example, and/orpreventing movement between the PCB 1922 and the sensing element 1920with respect to each other.

The contact resistance between the sensing element 1920 and PCB 1922 canbe measured and tested by accessing test pads on the PCB 1922. Forexample, in one embodiment, the PCB 1922 includes three discontinuous,aligned test pads that overlap two contact portions between the PCB 1922and sensing element 1920. A drive current is applied, and the voltagedrop across the test pads is measured. For example, in one embodiment, adrive current of about 100 mA is provided. By measuring the voltage dropacross the test pads the contact resistance can be determined by usingOhm's law, namely, voltage drop (V) is equal to the current (I) througha resistor multiplied by the magnitude of the resistance (R), or V=IR.While one method for attaching the shield layers 1926, 1928, the bondinglayer 1924, the sensing element and the PCB 1922 to the frame 1918 hasbeen described, other methods are possible. For example, as discussed,in some embodiments, one or more of the various separate layers arecombined in an integral layer which is attached to the frame 1918 in onestep.

Printed Circuit Board

The PCB 1922 includes various electronic components mounted to either orboth faces of the PCB 1922. When sensor assembly is assembled and thePCB 1922 is disposed in the upper frame cavity 1930, some of theelectronic components of the PCB 1922 may extend above the upper framecavity 1930. To reduce space requirements and to prevent the electroniccomponents from adversely affecting operation of the sensor assembly,the electronic components can be low-profile, surface mounted devices.The electronic components are often connected to the PCB 1922 usingconventional soldering techniques, for example the flip-chip solderingtechnique. Flip-chip soldering uses small solder bumps such ofpredictable depth to control the profile of the soldered electroniccomponents. The four tabs 1968 of the inner copper shield 1926 and theupper planar portions 1973 of the outer copper shield 1928 are solderedto the PCB 1922 in one embodiment, electrically coupling the electricalshielding barrier to the PCB 1922.

In some embodiments, the electronic components include filters,amplifiers, etc. for pre-processing or processing a low amplitudeelectric signal received from the sensing element 1920 (e.g., theoperational amplifiers discussed above with respect to the Faraday cage)prior to transmission through a cable to a physiological monitor. Inother embodiments, the electronic components include a processor orpre-processor to process electric signals. Such electronic componentsmay include, for example, analog-to-digital converters for convertingthe electric signal to a digital signal and a central processing unitfor analyzing the resulting digital signal.

In other embodiments, the PCB 1922 includes a frequency modulationcircuit having an inductor, capacitor and oscillator, such as thatdisclosed in U.S. Pat. No. 6,661,161, which is incorporated by referenceherein. In another embodiment, the PCB 1922 includes an FET transistorand a DC-DC converter or isolation transformer and phototransistor.Diodes and capacitors may also be provided. In yet another embodiment,the PCB 3114 includes a pulse width modulation circuit.

In one embodiment, the PCB 1922 also includes a wireless transmitter,thereby eliminating mechanical connectors and cables. For example,optical transmission via at least one optic fiber or radio frequency(RF) transmission is implemented in other embodiments. In otherembodiments, the sensor assembly includes an information element whichcan determine compatibility between the sensor assembly and thephysiological monitor to which it is attached and provide otherfunctions, as described below.

Additional Example Sensor

FIG. 23A is a top perspective view illustrating portions of anotherembodiment of a sensor system 2300 including a sensor assembly 2301suitable for use with any of the physiological monitors shown in FIGS.1A-C. The sensor assembly 2301 includes a sensor 2315, a cable assembly2317 and a connector 2305. The sensor 2315, in one embodiment, includesa sensor subassembly 2302 and an attachment subassembly 2304. The cableassembly 2317 of one embodiment includes a cable 2307 and a patientanchor 2303. The various components are connected to one another via thesensor cable 2307. The sensor connector 2305 can be removably attachedto a physiological monitor (not shown), such as through a monitor cable,or some other mechanism. In one embodiment, the sensor assembly 2301communicates with a physiological monitor via a wireless connection.

The sensor system 2300 and certain components thereof may be generallysimilar in structure and function or identical to other sensor systemsdescribed herein, such as, for example, the sensor systems 100, 1900described herein with respect to FIGS. 1 and 19-22, respectively.

For example, the sensor system 2300 may include an electrical shieldingbarrier (FIGS. 23D-E) including one or more layers which form a Faradaycage around an piezoelectric sensing element (FIGS. 23D-E), and whichdistribute external electrical noise substantially equally to electricalpoles of the piezoelectric sensing element. The shielding barrier orportions thereof of some embodiments can flexibly conform to the surfaceshape of the piezoelectric element as the surface shape of thepiezoelectric element changes, thereby improving the shielding andsensor performance.

The sensor system 2300 may further include an acoustic coupler 2314which can including a bump positioned to apply pressure to the sensingelement so as to bias the sensing element in tension. The acousticcoupler can also provide electrical isolation between the patient andthe electrical components of the sensor, beneficially preventingpotentially harmful electrical pathways or ground loops from forming andaffecting the patient or the sensor.

The sensor system 2309 may also include an attachment subassembly 2304.In one embodiment, the attachment subassembly 2304 is configured topress the sensor against the patient's skin with a pre-determined amountof force. The attachment subassembly 2304 can be configured act in aspring-like manner to press the sensor 2300 against the patient. Theattachment subassembly 2304 can also be configured such that movement ofthe sensor 2300 with respect to the attachment subassembly 2304 does notcause the attachment subassembly 2304 to peel off or otherwise detachfrom the patient during use.

Additionally, in some embodiments, a patient anchor 2303 is providedwhich advantageously secures the sensor 2315 to the patient at a pointbetween the ends of the cable 2307. Securing the cable 2307 to thepatient can decouple the sensor assembly 2300 from cable 2307 movementdue to various movements such as accidental yanking or jerking on thecable 2307, movement of the patient, etc. Decoupling the sensor assembly2300 from cable 2307 movement can significantly improve performance byeliminating or reducing acoustical noise associated with cable 2307movement. For example, by decoupling the sensor 2300 from cablemovement, cable movement will not register or otherwise be introduced asnoise in the acoustical signal generated by the sensor 2300.

The shielding barrier, acoustic coupler 2314, attachment subassembly2304, and patient anchor 2303 may be generally similar in certainstructural and functional aspects to the shielding barrier, acousticcoupler 1914, attachment subassembly 1904, and patient anchor 1903 ofother sensor systems described herein, such as the sensor system 1900described with respect to FIGS. 19A-22B, for example.

FIGS. 23B-C are top and bottom perspective views of a sensor includingsubassembly 2302 and an attachment subassembly 2304 in accordance withanother embodiment of the present disclosure. The attachment subassembly2304 generally includes lateral extensions symmetrically placed aboutthe sensor subassembly 2302. An embodiment of a similar attachmentsubassembly is described in detail with respect to FIG. 10.

FIG. 23D-E are top and bottom exploded, perspective views, respectively,of the sensor subassembly of FIGS. 23A-C. The frame 2318 generallysupports the various components of the sensor such as the piezoelectricelement, electrical shielding barrier, attachment element and othercomponents. The sensor subassembly 2302 includes an acoustic coupler2314, sensing element 2320, adhesive layer 2324, and first and secondelectrical shielding layers 2326, 2328 which may, in certain aspects, begenerally similar in structure and function to the acoustic coupler1914, sensing element 1920, adhesive layer 1924, and first and secondelectrical shielding layers 1926, 1928 of FIGS. 19A-19E, for example.

As shown, and unlike the embodiment shown in FIGS. 19A-E, the adhesivelayer 2324 of FIG. 23D-E stretches straight across the frame 2328without conforming to the surface 2350 on the underside of the frame2318. Thus, the sensing element 2320 is sandwiched between the adhesivelayer 2324 and the outer shielding layer 2328. The adhesive layer 2324includes adhesive over its entire outer surface which is in contact withthe sensing element 2320. Moreover, the copper layer 2328 may alsoinclude an adhesive on its interior surface which contacts the otherside of the sensing element 2320. As such, the adhesive layer 2324 andthe shielding layer 2328 bond to opposite sides of the sensing element2320, sandwiching and creating a seal around it. This sandwiching andsealing of the sensing element 2320 improves the liquid resistivity ofthe sensor subassembly 2302 by impeding water or water vapors (e.g.,from sweat or other sources) from ingressing and contacting the sensingelement 2320. Thus, the sandwiching of the sensing element 2320 protectsthe sensor 2302 from undesired effects such as electrical shorting dueto liquid ingress. In one embodiment, the sensor 2302 is IPX1 compliant.

The planar portion 2325 of the adhesive layer 2324, along with thecorresponding planar portions 2321, 2329 of the sensing element 2320 andouter shielding layer 2328, are configured to move with respect to thecavity defined by the underside of the frame 2318 in response tovibrations. The adhesive layer 2324 generally includes adhesive on allof its surface area except for the interior surface of the planarportion 2325. As such, the adhesive layer 2324 is securely bonded inplace while the planar portion 2325 can move freely with respect to thecavity during operation without sticking. Moreover, because the interiorportion of the planar portion 2325 is non-adhesive, foreign materialsuch as dust particles will generally not stick to the non-adhesiveplanar portion 2325, improving sensor operation.

Similar to the frame 1918 of FIG. 19D, the frame 2318 includes fourlocking posts 2332. However, the posts 2332 of FIG. 23D are shown in alocked or liquefied configuration, unlike the posts 1932 illustrated inFIG. 19D.

As shown in FIG. 23D, the shielding layers 2326, 2328 include flapportions 2368, 2373 which conform to the frame 2318 and sit underneaththe PCB 2322 in an assembled configuration. Similarly, the sensingelement 2320 of the sensor subassembly 2302 includes a flap portion 2372which conforms to the frame 2318 and sits underneath the PCB 1922. Uponwelding of the locking posts 2332, the PCB 2322 is pressed downwardsinto physical and electrical contact with the flap portions 2368, 2373,2372 of the shielding layers 2326, 2328 and sensing element 2320. Assuch, because the flaps 2368, 2373, 2372 are configured to situnderneath the PCB 2322, they are held in place in a pressure fitwithout soldering, improving manufacturability.

Information Element

In addition, the sensor assembly can include any of a variety ofinformation elements, such as readable and/or writable memories.Information elements can be used to keep track of device usage,manufacturing information, duration of sensor usage, compatibilityinformation, calibration information, identification information, othersensor, physiological monitor, and/or patient statistics, etc. Theinformation element can communicate such information to a physiologicalmonitor. For example, in one embodiment, the information elementidentifies the manufacturer, lot number, expiration date, and/or othermanufacturing information. In another embodiment, the informationelement includes calibration information regarding the multi-parametersensor. Information from the information element is provided to thephysiological monitor according to any communication protocol known tothose of skill in the art. For example, in one embodiment, informationis communicated according to an I²C protocol. The information elementmay be provided on or be in electrical communication with the PCB 1922.In various embodiments, the information element can be located inanother portion of the sensor assembly. For example, in one embodiment,the information element is provided on a cable connected to the PCB1922. The information element may further be located on the sensorconnector 1905, the attachment subassembly 1904, or some other part ofthe sensor assembly.

The information element can include one or more of a wide variety ofmemory devices known to an artisan from the disclosure herein, includingan EPROM, an EEPROM, a flash memory, a combination of the same or thelike. The information element can include a read-only device such as aROM, a read and write device such as a RAM, combinations of the same, orthe like. The remainder of the present disclosure will refer to suchcombination as simply EPROM for ease of disclosure; however, an artisanwill recognize from the disclosure herein that the information elementcan include the ROM, the RAM, single wire memories, combinations, or thelike.

The information element can advantageously store some or all of a widevariety data and information, including, for example, information on thetype or operation of the sensor, type of patient or body tissue, buyeror manufacturer information, sensor characteristics includingcalculation mode data, calibration data, software such as scripts,executable code, or the like, sensor electronic elements, sensor lifedata indicating whether some or all sensor components have expired andshould be replaced, encryption information, monitor or algorithm upgradeinstructions or data, or the like. In some embodiments, the informationelement can be used to provide a quality control function. For example,the information element may provide sensor identification information tothe system which the system uses to determine whether the sensor iscompatible with the system.

In an advantageous embodiment, the monitor reads the information elementon the sensor to determine one, some or all of a wide variety of dataand information, including, for example, information on the type oroperation of the sensor, a type of patient, type or identification ofsensor buyer, sensor manufacturer information, sensor characteristicsincluding history of the sensor temperature, the parameters it isintended to measure, calibration data, software such as scripts,executable code, or the like, sensor electronic elements, whether it isa disposable, reusable, or multi-site partially reusable, partiallydisposable sensor, whether it is an adhesive or non-adhesive sensor,sensor life data indicating whether some or all sensor components haveexpired and should be replaced, encryption information, keys, indexes tokeys or has functions, or the like monitor or algorithm upgradeinstructions or data, some or all of parameter equations, informationabout the patient, age, sex, medications, and other information that canbe useful for the accuracy or alarm settings and sensitivities, trendhistory, alarm history, sensor life, or the like.

Terminology/Additional Embodiments

Embodiments have been described in connection with the accompanyingdrawings. However, it should be understood that the figures are notdrawn to scale. Distances, angles, etc. are merely illustrative and donot necessarily bear an exact relationship to actual dimensions andlayout of the devices illustrated. In addition, the foregoingembodiments have been described at a level of detail to allow one ofordinary skill in the art to make and use the devices, systems, etc.described herein. A wide variety of variation is possible. Components,elements, and/or steps can be altered, added, removed, or rearranged.While certain embodiments have been explicitly described, otherembodiments will become apparent to those of ordinary skill in the artbased on this disclosure.

Conditional language used herein, such as, among others, “can,” “could,”“might,” “may,” “e.g.,” and the like, unless specifically statedotherwise, or otherwise understood within the context as used, isgenerally intended to convey that certain embodiments include, whileother embodiments do not include, certain features, elements and/orstates. Thus, such conditional language is not generally intended toimply that features, elements and/or states are in any way required forone or more embodiments or that one or more embodiments necessarilyinclude logic for deciding, with or without author input or prompting,whether these features, elements and/or states are included or are to beperformed in any particular embodiment.

Depending on the embodiment, certain acts, events, or functions of anyof the methods described herein can be performed in a differentsequence, can be added, merged, or left out all together (e.g., not alldescribed acts or events are necessary for the practice of the method).Moreover, in certain embodiments, acts or events can be performedconcurrently, e.g., through multi-threaded processing, interruptprocessing, or multiple processors or processor cores, rather thansequentially.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein can be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. The described functionalitycan be implemented in varying ways for each particular application, butsuch implementation decisions should not be interpreted as causing adeparture from the scope of the disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein can be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor can be a microprocessor, but in thealternative, the processor can be any conventional processor,controller, microcontroller, or state machine. A processor can also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The blocks of the methods and algorithms described in connection withthe embodiments disclosed herein can be embodied directly in hardware,in a software module executed by a processor, or in a combination of thetwo. A software module can reside in RAM memory, flash memory, ROMmemory, EPROM memory, EEPROM memory, registers, a hard disk, a removabledisk, a CD-ROM, or any other form of computer-readable storage mediumknown in the art. An exemplary storage medium is coupled to a processorsuch that the processor can read information from, and write informationto, the storage medium. In the alternative, the storage medium can beintegral to the processor. The processor and the storage medium canreside in an ASIC. The ASIC can reside in a user terminal. In thealternative, the processor and the storage medium can reside as discretecomponents in a user terminal.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the devices or algorithms illustrated can be madewithout departing from the spirit of the disclosure. As will berecognized, certain embodiments of the inventions described herein canbe embodied within a form that does not provide all of the features andbenefits set forth herein, as some features can be used or practicedseparately from others. The scope of certain inventions disclosed hereinis indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. An acoustic sensor system comprising: a firstacoustic sensor comprising: a first inner layer; a first sensingelement; and a first outer layer; and a second acoustic sensorcomprising: a second inner layer; a second sensing element; and a secondouter layer, wherein the first and second acoustic sensors are arrangedin a stack, wherein the first and second inner layers are positionedbetween the first and second sensing elements, wherein the first andsecond sensing elements are positioned between the first and secondouter layers, and wherein the first and second outer layers areconfigured to shield the first and second inner layers fromelectromagnetic noise.
 2. The acoustic sensor system of claim 1, whereinthe first and second outer layers are coupled to a common potential. 3.The acoustic sensor system of claim 2, wherein the first and secondsensing elements comprise piezoelectric elements.
 4. The acoustic sensorsystem of claim 3, wherein the first and second inner layers and thefirst and second outer layers comprise electrode coatings.
 5. Theacoustic sensor system of claim 4, wherein the first inner layer coversa first percentage of an inner surface area of the first sensingelement, and wherein the first outer layer covers a second percentage ofan outer surface area of the first sensing element, the secondpercentage greater than the first percentage.
 6. The acoustic sensorsystem of claim 5, wherein the second inner layer covers a thirdpercentage of an inner surface area of the second sensing element, andwherein the second outer layer covers a fourth percentage of an outersurface area of the second sensing element, the fourth percentagegreater than the third percentage.
 7. The acoustic sensor system ofclaim 6, wherein the first acoustic sensor produces a first signal inresponse to acoustic vibrations and provides the first signal to a noiseattenuator, and wherein the second acoustic sensor produces a secondsignal in response to acoustic vibrations and provides the second signalto the noise attenuator, wherein the noise attenuator is responsive tothe first and second signals to produce a reduced noise signal having ahigher signal to noise ratio than either of the first or second signals.8. The acoustic sensor system of claim 7, wherein the first and secondouter layers distribute electromagnetic noise incident on the acousticsensor system substantially evenly between the first signal and thesecond signal.
 9. The acoustic sensor system of claim 8, wherein theelectromagnetic noise in the first signal is substantially in phase withthe electromagnetic noise in the second signal.
 10. The acoustic sensorsystem of claim 9, further comprising an intermediate layer positionedbetween the first and second inner layers, the intermediate layerconfigured electrically insulate the first and second acoustic sensorsfrom one another.
 11. The acoustic sensor system of claim 10, whereinthe intermediate layer forms a substantially water resistant sealbetween the first and second acoustic sensors.
 12. The acoustic sensorsystem of claim 11, wherein the intermediate layer is configured to atleast partially bond the first and second sensors together such thatmechanically active regions of the first and second sensing elementsmove together in response to acoustic vibrations.
 13. The acousticsensor system of claim 4 further comprising: a noise attenuator coupledto the first inner layer of the first acoustic sensor and the secondinner layer of the second acoustic sensor, the noise attenuatorconfigured to: at least partially constructively combine a physiologicalsignal component of a first signal output by the first acoustic sensingelement and a physiological signal component of a second signal outputby the second acoustic sensing element; and at least partiallydestructively combine a noise component of the first signal output bythe first acoustic sensing element and a noise component of the secondsignal output by the second acoustic sensing element.
 14. The acousticsensor system of claim 13, wherein the noise attenuator comprises atleast one of: circuitry including an amplifier, a signal processor, or ageneral-purpose processor.
 15. The acoustic sensor system of claim 14,wherein the noise attenuator is further configured to generate a reducednoise signal based on constructively combining the physiological signalcomponents and destructively combining the noise components.
 16. Theacoustic sensor system of claim 15, wherein the reduced noise signal hasa lower noise component than one or more of the first and secondsignals.
 17. The acoustic sensor system of claim 16, wherein the noiseattenuator generates the reduced noise signal using common-moderejection.
 18. A method comprising: receiving signals from an acousticsensor system according to claim 1 that is attachable to a medicalpatient and configured to provide the signals responsive to acousticvibrations indicative of one or more physiological parameters of themedical patient.
 19. The method of claim 18, wherein the acoustic sensorsystem further includes a coupling bump configured to apply pressure toat least one of the first and second sensing elements to push at least aportion of the one of the first and second sensing elements into acavity of the acoustic sensor system.
 20. The method of claim 19,wherein the coupling bump is configured to transmit acoustic vibrationsto the one of the first and second sensing elements through the acousticcoupling bump when the acoustic sensor is attached to the medicalpatient.